I our bedroom, where I do most of my music listening, I have the following system that also acts as the computer sound.  Like many of you, I am planning to upgrade (before the end of the year).  I like to plan ahead, so my question is what would you upgrade in this system?
Sony CDP-CE500 (my newest item) CD player
Technical Pro PRE-B5050 preamp
AudiosSource Model Amp One/A power amp
Polk RTi4 bookshelf speakers
Sony SA-W2500 subwoofer (only playing what the Polks can't)
By the end of the year, I should have between $250 to $350 to spend.  Should I get an AVR?  Should I get a better sub?
The preamp is actually designed for a DJ.  It was the only one I could find at that time that was not a total cheapo (Pyle, Pyramid) or $400 (or more).  I like how it sounds now, but I am enough of an audiophile to want better.  I like the highs and mids of the Polks and the other speakers I sometimes use.  Most of my listening is nearfield, about 29 inches from the speakers, which sit on stands on the back of a computer table, one behind the printer, one behind the PC tower, sub on the floor under the table.  I know it is up to me; I just want to know what some of you would upgrade.  Peace and goodwill.