Actually 320 kbps is pretty darn good but if you are ripping music using a computer, you might as well use a lossless format since hard disc space is cheap.
Do you want to stream this from a computer wirelessly or do you want an MP3 player (like an iPod)? You can get very good sound from an iPod but you have 2 choices, cheap and not so cheap. Cheap (and pretty good) is to use the MP3 (or iPod dac). With an iPod, for example, you'll want to use the line out via the dock connector with something like this,
Amazon.com: FiiO L9 L-Shaped Line Out Dock (LOD) Cable For iPod and iPhone: MP3 Players & Accessories. More expensive and probably better is to bypass the iPod's dac with an external unit. I like this unit from HRT because I like HRT products and because it will work with a variety of different dock connections:
Amazon.com: HRT iStreamer Outboard DAC for iDevices: Electronics
Alternatively, if you want to go wirelessly, there are tons of different solutions. You can love or hate Apple, but iTunes works well and it can stream nicely to an Apple TV or an Apple express (which is also works as a repeater for your wifi). You will want to use an external dac with these because they don't sound that great from the line out. But they tend to be expensive (esp. for what they do) and most will blow through your $300 budget pretty fast.
There is a third option. You could just get the Onk TX 8050 networking stereo receiver:
Amazon.com: Onkyo TX-8050 Network Stereo Receiver (Black): Electronics. It fits your budget, it will stream music, and it has a usb input for playback from an iPod or a hard disc. This may be your most cost effective solution.
