Streaming through upconverting DAC - can I even improve audio quality?

I don’t mean to pick on the OP or engage in Audio Heresy, but it’s interesting that he has been listening to a compromised source, namely Spotify Free, and enjoying it. It isn’t until others have been pointing out how compromised his source is that he is starting to become seriously concerned. Now, the OP states he is a veteran listener, and speaking as someone who just flunked his hearing test, some of that may be due to an age related loss in auditory acuity. However it is more likely that Spotify is doing its job with its algorithm.

I have spent a large chunk of my background listening the last 10 years to a radio station, Radio Venice, that sounds pretty good. Fire up a CD on the same system and the improvement becomes obvious, but listening in isolation, I can and have whiled away time listening with much pleasure. I was surprised to discover, when I purchased a streamer that displayed bit rates, that it broadcasts at 128 bps. Listening critically I can tell that my local Classical station, WFMT, which broadcasts at 320 bps, sounds better, in terms of more air around the musicians. However, instrumental tone is largely preserved at the lower bit rate. I always thought that iTunes over a mid Fi system or headphones sounded pretty good. There are some low bit rate stations however that sound awful. The BBC Radio3 probably sounded better to the French Resistance listening clandestinely in WW II than I can get. I don’t think that bit rates tell the entire story. There have to be differences in the algorithms that make a significant determinant in audio quality.  I used to subscribe to Spotify years ago and always thought they sounded pretty good, and remember thinking that Ogg Vorbis must be a superior compression system.

My main experience with upsampling comes from a DAC that I used about 15 years ago, when I know my hearing was better. It would upsample to 96 and 192 I listened mainly to CDs sourced from whatever my CD player was back then. I remember for the most part being impressed by the lower upsampling setting. It seemed to expand the soundstage, particularly in the front to back positioning of the Orchestra. The higher upsampling rate however sounded off from the get go. It seemed like the same soundstage was moth eaten, as if there were gaps in it. Eventually I just went fo no upsampling.

Native / pure DSD - yes, it sounds good. Upsampling - so so. I don't bother with it (using a Teac NT-505, Topping E30ii, etc DAC).

The Marantz SA-10 has two USB inputs but they cannot be used for streaming and both are synchronus.  One is a USB -A used strictly for stored music and the other is USB-B which is dedicated to iPod input, and older versions at that.  The SA-10 is unfortunately dated in this USB respect although from what I read unless a DAC is uber expensive most of the streamers sound better through COAX.  I think the method of streaming USB vs. COAX also has something to do with the clocks in both units and which one dominates in each of the two methods, but I'm not sure.  I know the Marantz has two femto streamers and the ifi has one. The SA-10 does have an optical streamer input but the ifi Zen Stream does not have an optical output.  Just because the SA-10 manual is a little confusing, I connected the ifi Zen Stream via both USB inputs and got nothing.  Anyway, my goal in getting the SA-10 was to make sure I had a high end SACD player and I liked the idea that, like the PS Audio Direct Stream, which went out of production at the time because it used a Toshiba disc drive, of converting and upscaling everything to DSD.  The fact that the SA-10 allowed streaming at all I considered a bonus if I were to try streaming.  My first attempt was to use a usb cable from my Macbook Air laptop and be able to sit across the room so I invested in a long usb cable and thought the sound was decent, but not good.  The next goal was to try a dedicated streamer at a minimal investment so I found a new ifi Zen Stream for $275 and that sounded good.  Then, of course I had to read more and found linear power supplies make a difference so for a few hundred bucks got the ifi version from Amazon.  No question the sound improved.  I made sure I had a true 75 ohm SPIDF cable.  My goal in all of this was to use the setup to preview music and then if I really, really like it, buy it on disc.  Now, however, I found the streaming setup sounds really good, even on free Spotify with its low bit rate lossy transmission.  No doubt the "Dac-less dac" in the SA-10 with its proprietary Marantz MMM conversion and DSD output has something to do with that.  I'm guessing for the investment what I'm getting is pretty close to optimal free Spotify sound.  So those goals have been achieved.  Now, the next step is to do some more critical listening as best as I am equipped) to compare cd and the streaming setup and then see what changes with Quobuz.  I don't buy that many CD's or SACD's anymore so I can then consider a Quobuz subscription to break the disc habit.  Whether it pays for me to take a next step to another DAC or streamer or combination might be questionable at that point and the investment spectrum is wide open.  I am intrigued with the new Eversolo DMP-8 because at its price point it would enable me to compare the AKM chip dac sound to the Marantz.  Plus if I can figure out the connections the Luxman has two sets of balanced inputs.  One would be used for the current setup with the Eversolo streaming through the Marantz DAC and the other can connect to the Eversolo DMP-A8's balanced inputs.  The Luxman then with its front selector dial lets either of its balanced inputs be used as an integrated amp or just as a power amp.  So the Eversolo could then be used with the Luxman power amp.  The Marantz SA-10 also has digital outputs and the Eversolo DMP-A8 has digital inputs so the system can be connected that way, too.  There are so many ways to see what sounds like what I think it would be very interesting. 

Completely untrue usb with a good streaming device and cable with a high res source puts spdif to shame also the marantz website says the usb can hook up to a pc. https://manuals.marantz.com/SA10/NA/EN/WBSPSYdzpskctb.php

And the sa 10 is asyncronous

https://manuals.marantz.com/SA10/NA/EN/WBSPSYdzpskctb.php

From marantz directly The SA-10 is designed to set a new standard in audio. Whether listening to ... Asynchronous mode rear USB, Yes. Bit-perfect transmission, Yes. Signal

Yes, I can use my Macbook Air and did.  I wanted to hardwire ethernet but use the computer from across the room so I purchased a 25 or 30 ft. usb a to usb b cable with an inline booster.  There was also the need for a uab c to usb a connector since the Mac only has usb c.  This was in my living room so I was getting the data stream to the Mac vis the computer's Wifi 5.  The ifi streamer is connected via ethernet to the modem/gateway.  So then, when I use the MAC wirelessly it is sends the signal over ethernet to the ifi.  For whatever reason, the ifi sounds much better than the usb directly to the Marantz although its been a while since I listened that way and I never tried the setup with a shorter usb from the computer to the Marantz.  It's just too inconvenient to do that and sit in the sweet spot on the other side of the room.  I thought I had read synchronous, but I guess I was mistaken.  However, the way the Marantz is made its USB inputs are for connection to a computer or a memory device/stick or for files stored on an ipod or iphone.  For connecting to a device with digital outputs, i.e.digital streams, and using the Marantz as a DAC, the digital inputs on the SA-10 are only coax or optical.  The ifi Zen Stream has 2 usb-a 3.0 outputs and I tried both into both the Marantz usb-a and usb-b inputs and it does not work.  I thought that was a synchronous/asynchronous issue but it's something else in the way that handshake has to be configured that simply was not designed into the SA-10.  The word "streamer" is absolutely not mentioned once in the SA-10 manual.  I'm not technical enough to understand how the SA-10 is engineered to only take a digital in signal via coax, but unless I'm missing something or there's some magic trick or device to insert between the ifi usb output and one of the SA-10's usb inputs to allow it to stream that way, it's only coax for streaming through the SA-10.