have 2 pairs of them..really like them alot( i own the original and the upgraded). there are 3 differnt series of them that i am aware of.
1. original- serial serial numbers on sticker on the back.
2. upgraded- different caps, upgraded internal wire, bias adjust and removal mod of circut protection. you can tell by the serial number stickers- it is on the bottom.
3. signature series - 2 power switches and regualted power supply (very rare)
the amps were popular during the ninties. dean of pse keeps a low profile and doesnt advertise much. he is really nice guy and very talented engineer.
as far as for sonic signature - very neutral of what is being feed to them and balls to wall bass / dynamics/and awesome microdynamics. i would consider them one slight step below the herron mono blocks. they sound best in the balanced mode imo.
there was a pair on ebay with the pse studio III tunere that didnt sell. the seller should have seperated the pieces ad took better shots.
as far as for price i bought two pairs in 2003. the blue book is $670.
hope that helps,