Keep the iRiver. It works.. if it ain't broke...
Get a P48 tinybox ($199) from Naiant (www.naiant.com or "Jon Stoppable" on this board)
In the $399 range for used gear, look for Busman BSC1 (the 2s are $900 new and probably out of your range used), Avantone CK1, Studio Projects C4s (these can be had for about $199 used if you're lucky), Rode NT5s (I think a new set is like $400-450), AKG 391s, etc. Any decently-built small diaphragm condenser that you see guys on this board using can certainly do the trick.
Then get Ted Gakidis or Darktrain [is Robb selling cables right now?] to do a cable to run the mics into the tinybox.
Done.