Whats the difference ...

First, if you find something you like the sound of, stick with it!

The all-in-one machines provide convenience above all else, but there’s a big difference in the user interface, that is, the software as well as possibly the sound quality. They could be better sounding, or could be worse. Truth is the Oppo’s had great sounding DACs and while some combination units may be better, they may also not be.

Personally, I’d say that the big reason to look for a change from where you are is usability and fewer pieces of gear in your rack.

Not a fan of all in one units personally — too limiting and inflexible.  If I was you I’d upgrade to a better streamer first (maybe like Innuos Pulse Mini with upgraded LPS from Teddy Pardo) and then the DAC.  You’ve got a nice preamp so not sure you’d wanna switch that out for a combo pre.  Also, JPLAY is reputed to sound better than mconnect if you wanna do a free trial to see if it makes a difference.  Just my $0.02 FWIW.

There are some nice affordable all-in-one systems out there. I am not a fan of wasting money in the long run as most of us are so I preferred to buy separates. This way when your streaming transport goes out you can replace it. I use the BlueSound NODE. It does have a DAC but I prefer the DAC in my OPPO 205. Eventually I will upgrade but I’m very happy with the BlueSound APP. I can use MConnect through the OPPO to stream but I really like the BSN APP as a lot of people do. One of the big advantages is you are not stuck with a certain brand or sound. Plus DACs are like computers. There’s always a better one around the corner. Sometimes for less money. I’m not sure why you’re not just using your OPPO 105 as your streamer and your DAC. It should be very good. That being said multiple components means more space, more power cords, more interconnects, and finally, sometimes more cost. It’s all about the quality of sound and the ease of use. If you do get the BSN just buy a used 2i for $200 instead of the NODE for $450 on sale. When I decide on the sound or app I’m looking for the NODE will not be wasted. It will replace one of my old SONOS streamers. Try just using the OPPO 105 or see if you can try a BlueSound product feeding into your Schiit. I hope this helped. 

Engineering corners have to be cut in order to make those units affordable and fit into one box, so the differences are not always apparent or discernible from the specifications. Quality power and shielding between analog and digital components is probably the first thing to go. There are high end combo units that do address these factors, but they may not be considered affordable by many.

Audiophiles like separates for their singular focus and the ability to upgrade piecemeal when upgrade fever strikes and budgets allow. I agree with others you might want to try a streamer upgrade, Innuos is a safe bet, I would leapfrog over the Bluesound. I have a Gungnir myself, which I have recently replaced, it is a very good DAC in that price range. If you have not done the multibit upgrade, I highly recommend it. 
 

very much depends on the role streaming plays in your listening, both as relates to sound quality and software ease of use...I also use an Oppo 105, but thinking my small, inexpensive WiiM might sound better into a good DAC like you have...

@hsounds I did indeed use my Oppo as a streamer for years, but then the app interface went down and Oppo no longer supports the 105 or the app; thus I had to find a workaround. 

@soix @erik_squires Thanks for the words of wisdom and for putting things into perspective. 

@zlone yes, the Multibit upgrade is on the horizon - once I get my retip Hana cartridge back and paid for!