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.
dadork
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.
@dadork
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. 
I would begin with a separate 2- channel preamp with HT Bypass. Run all your music sources through it and the L/R preouts from your AVR into the bypass input. Used preamps on Audiomart from Rogue, Odyssey, VTL, etc. can be quite affordable and will get you going. Ditto on Node 2i for streaming. This assumes the Denon has L/R preouts. If not replace it with one that does 
Hi,
First of all, if you have an Apple computer get Channel D's Pure Music program. If you have a PC get J River's program. If you do not have one already get a good USB DAC, there are many on the market. You are already getting rid of the MP3 files. I generally use HDTracks for down loads. Next sell the Polks and get a pair of Klipsh Cornwall IV's This will make you VERY happy for a while. When more money comes in down the line get either a DEQX Premate or Anthem STR . These are digital preamplifiers with huge power. Next comes an amplifier. With the Cornwalls you only need 100 watts/ch and I would recommend a tube amp such as a Carver, Manley or Mcintosh. Finally, two subwoofers. You would already have the best crossovers in the preamps plus room control so all your need is a passive sub. If you are handy, building a sub from Parts Express would be tops and very cost effective. Now you can just collect music:)