Newbie Looking for Advice on Streaming Music

You will need two things, and sometimes they come in one box. You will need a streaming device and a DAC. Simple to use streaming devices could be an Apple Airport Express, a Sonus Connect or a Google Chromecast Audio. Personally I prefer these units to dedicated audiophile streamers because these three are from brands with such a market penetration that each and every streaming service will have to provide an App - you are not locked in. These three all have an inbuilt DAC, and to be honest pretty good ones. So you could start with them and use their internal DACs first, to see if you like the system. In my own case, I use Chromecast Audio players in a number of diferent set ups, and I am rather pleased. Even in my main system with Quad 2805 electrostats the sound is very good. This of course is not surprising, given the excellent measured results with 16/44 (i.e cd quality) recordings. See here for measurements: http://archimago.blogspot.nl/2016/02/measurements-google-chromecast-audio.html
The Airport Express measures similarly well, but it is perhaps slightly less convenient because it needs continued contact with your tablet or smartphone: http://www.kenrockwell.com/apple/airport-express-audio-quality-2014.htm
If you think you can get better audio quality, you can get a DAC with optical input (all three streamers that I mentioned have optical outputs as well and produce bitperfect and hence identical digital output). Here, the sky is the limit, but the million dollar question is whether you will hear the difference, as differences will be minute at best. The Pioneer U-05 would be a very good DAC at a reasonable price, the Benchmark DAC 3 defines the high end of the market, and an Oppo UD 205 UHD Bluray player may be a very practical option, as it combines pre amplifier, UHD multi format disc player and DAC with external inputs. If you also want digital room equalization the new DSpeaker Antimode X4 will give you that, plus automatic crossover setting between main speakers and subwoofers. All four of these DACs have variable outputs (i.e. a volume control) so they can serve as pre amplifiers, but not all of them still have analogue inputs for legacy gear like turntables.
But if I compare the sound quality of even the analogue output of a Chromecast Audio with that of a good turntable like my Linn Sondek LP12, it is obvious that the 16/44 stream is far superior.

As I said above, a DAC with a variable ouput is a perfect pre amplifier, but many do not have analogue inputs. I don't care, but others do. If you go that route, all you need is a power amplifier. Many of these DACs will have balanced ouputs, and if that is what you have, get a power amplifier that also has balanced connections. My preference is for beefy solid state amps. The more power the better, and solid state amps usually perform rather better/more neutral under real speaker loads (see the graphs in Stereophile). Beefy solid state power amps do not need to cost an arm and a leg.

See here for a review of the Sonica DAC: http://archimago.blogspot.nl/search?q=sonica
Summary: it is a good one with two limitations: the analogue input is less than perfect and there is only one optical, coaxial and usb input each. Try to connect a disc player, a tv and a Chromecast or other streamer and you are one input short.

I have no views on the PS Audio Jr other than that it is pretty pricey. I have not seen any proper tests with measurements done with serious lab gear like from Audio Precision. The currently best one on that is probably the Benchmark DAC3.
By and large I don't believe there are many meaningful sonic differences between well designed electronics, whatever the subjectivists on this forum want to believe. If there are differences, they are not necessarily for the better (e.g tube sound). The straight wire with gain criterion was met ages ago with solid state amplification, and I am increasingly inclined to believe that the same is now true for DACs. I am using the analogue output of the Chromecast Audio, and cannot hear any issues, even on a revealing system with Quad electrostats. Even if there may be a slight sonic degradation playing 16/44, it must be small, and I am also pretty sure that relatively affordable DACs like the Sonica, the Pioneer U-05 or the Teac UD-501 are as good as it can get. If you look at the measurement data for such DACs, you can see that frequency response, distortion and noise levels are mostly quite a bit better than for amplifiers, so they are not an problem. Electronic perfection has become pretty cheap, and there is nothing more perfect than perfect, given human hearing limitations. Those who believe they can hear differences between electronics are never able to repeat their insights under controlled conditions.
With electronics the three things that really matter are:
1 matching gain structure to avoid clipping. An example is the 2.0 Volt rca output of many digital sources and the too sensitive line inputs of many amplifiers.
2 insufficient power to prevent output clipping in dynamic music. In a largish room a few hundred watts per channel will do no harm.
3 load independent flat frequency response. Real speakers have varying impedances along the frequency spectrum, and some amplifiers' frequency response is far from flat under such realistic conditions (see the graphs in Stereophile - the audible limit of non-flatness is about 0.2 dB). Many tube amplifiers are very bad at this, hence their individual sonic signature, which is nothing other than an engineering shortcoming.
This is not to say that audio systems cannot be improved, but the weak links are the speakers, with their far bigger deviations from the flat frequency response, and much higher distortion that we would accept from any piece of electroncis. Finally, there is the issue of room interaction. Look at any in room response graphs and you will be horrified.

I personally think MQA is bogus, but if others prefer to believe otherwise that is up to them. Similarly I do not believe streamers themselves make much of a sonic contribution, if any. If there is one, it is in the DAC. For 16/44 all I can say that that is really not a serious challenge anymore for remotely decent DAC chip sets. So as long as streaming Tidal etc is only 16/44 there is little point in worrying too much.
For most people a DAC with variable ouput is a great pre amplifier, unless you insist on an analogue input (but for those there is e.g. the Marantz HD DAC1, plus of course the Benchmark DAC3 in a different price bracket).

In terms of streaming you are fine, esp. if you use the Chromecast's digital output. Its digital output has been shown to be bitperfect, and bitperfect is bitperfect. That digital  output is relatively jittery, but not to the extent that a good DAC could not deal with that.
You say you are also streaming from Win 7, I assume casting from a tab in Chrome on the computer. Sonically that is inferior to using the tablet or your phone to cast.