Steve - My 1/2 a cent. Maybe spend some $ on room treatment first. What you describe seems like it would be highly reflective. Damp it down & see what you got, then upgrade speakers if it's still not working for you.
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I would definitely encourage you to explore using Lossless files (.flac) if you've been using just typical bitrate itunes files or mp3's. You'd probably need a 160gb ipod classic or the 1st generation Apple TV's to be able to fit the same amount of music. That could make a big difference if you're not already there.
I'll also second Ghosts' idea of damping the room. Heavy curtains and a decently thick rug would be a nice start. If it's a step in the right direction, you could add some acoustic panels.
If you're not happy at that point, then start getting out and listening to some other gear.
if you're not already doing so, you'll want to connect your computer/iphone by usb to your outlaw--my recollection is that the inboard usb dac on the outlaw is pretty good and i'd go with that before trying an external dac. i'd second jazzerdave/kclone on assuring that you're listening to uncompressed files. finally, i'd address your speakers--lots of upgrade choices in the $500-800 range, esp. used (rega rs1, nht, triangle, focal chorus, psb imagine, etc.).