What to upgrade next.

This is my first foray into the forum other than reading other's post. I hope respondents will be kind! I am at the very low end of audiophile equipment and many of you may not think I am there yet when I list my equipment. The economy has become better for myself and I am looking to upgrade but not exactly sure where to go from here. I am sure I will receive many different suggestions so I plan on taking the one suggestion that I receive the most and employing it. My equipment is as follows: Denon AVRx 3500H as my integrated amp which is boosted by a Bob Carver Cinema Grand 5 which pushes 200wpc. This powers my Polk Audio RTiA7's which are my music floorstanders. When I started upgrading I chose the Polk's as they seem to punch above their weight. After months on this site I am unaware of many people who extol the virtues of the Polks so I am thinking this may receive the most as far as recommendations. I stream most of my music from my desktop and laptop. The desktop sounds like an airplane waiting to take off. I am not independently wealthy but am looking to spend between 2-3 thousand if necessary. The one thing that gives me the biggest headache at this point is music delivery as computers have glitches and my angina acts up when the music cuts out in the middle of Alex Lifeson shredding his axe. My music files range from bad copies of MP3s which are slowly being replaced to HD Audio files. Thank you for any suggestions.
Hi Dadork,

Because you’re operating your system for both music and movies, my advice will diverge from the stereo purists here.

1. Buy a leviton hospital grade 20A electrical outlet. $10

2. Buy a video streamer that will allow you to cast from your phone over WiFi--either the Chromecast Ultra or Nvidia Shield TV (which has chromecast built in). Both of these video streamers will allow you to cast movies and music from your phone. In addition to your personal HD tracks, I recommend subscribing to either Tidal or Qobuz to get CD quality and higher recordings. I use Qobuz and a chromecast ultra in my home theater. I also have a separate stereo system in the main room that I cast to.

3. Buy a low noise power supply for your video streamer. iFi has a variety of options to meet many voltage and amperage requirements.

These recommendations are super affordable, should increase sound quality, and will also level up your experience. These building blocks will also give you a good benchmark from which to judge future streamer/home theater bypass upgrades. 
A streamer and a good dac would do a lot. I don’t think it would be a waste. 
I would think a good DAC would be a great place to start. The Musical Fidelity V-90 is a real value for $299 new. And since you mention your desktop is noisy, you might look for a Software-based fan controller. My iMac In my listening room was very loud. Mac’s Fan Control lets you choose the RPM that cools while holding down the noise. I assume there’s something similar for PCs.
Welcome to the club. My general advice to you is to do a lot of research before you buy. When you finally do, buy second hand. Some of us are further up the chain than you are, but the feeling to upgrade is universal in this hobby. So take advantage of that. Keep in mind that price is not always proportional with sound quality although unfortunately it often is. So good luck, have fun and try to spend more time in front of your equipment than behind it.