What can I do to upgrade my system? Thanks


My current system right now is used for movies and music hooked up from my computer via optical cable from sound card built in to my motherboard. I listen to all genres of music and all different quality files from 256-lossless
I would say its 75% music and 25% movies on this system.

I was hoping someone could help me out with upgrading. What would be the cheapest upgrade that would give me noticeable gains in sound quality.

Here's my current system

Surround Front - Monitor Audio Silver Rx1's
Front Center - Monitor Audio BX centre
Rear Surround - Definitive Technology ProMonitor 800
Sub - Sony sa-wm250
Reciever/AMP - Denon AVR - 3805

My budget for upgrading is $400

I posted this on another forum and someone suggested I invest in a DAC(HRT music streamer pro) which started a debate in if a DAC would do anything since my Denon has a built in one. I figured this forum could help me out a little better. Also if a DAC wouldn't be my best option please let me know.
Thanks in advance
128x128bayvillian516
Thanks for all the responses.
My speaker wire I'm using is the lamp or extension cord wire from home depot. Would it be a noticeable difference if I upgraded that wire?

Its about 8-10 feet from my computer to the denon.
I'll look into the usb to spdif converter. What would a decent one be?
question one....change them today unless spending money results in less food for children in home or eviction due to not paying rent. there are many at low[er] prices like kimber,anti-cables, and morrow audio that once installed in your system will make you wonder why you waited.
question two...i found the wireworld ultaviolet usb good. the company claims low jitter etc. 49 dollars new
no kids, debt, or eviction on the horizon but I do like sticking to my rules of budgeting.
What would I plug that wireworld usb into?
thanks
Unless your computer is very quiet or your music very loud, I would remove the computer to another room and get a transport like a Squeezebox Touch or used Squeezebox Duet.
sorry . thought you had a seperate dac and looked again and saw you have a denon reciever with internal dac.