Which Speaker in the 4-6K Range?

You have to give a listen to the Sonus Faber Grand Pianos. They absolutely disappear and hit all of your requirements except price. They are actully less than you are looking to spend. If you are looking to buy used, you should listen to the more expensive speakers they make as well. They are phenominal.

Hi Kasboot. Your desription sounds like my Meadowlark Heron i speakers. They are 90.5db, go down to 25hz, sweet and warm. And they disappear. In fact, they are just amazing. They do everything with such ease, filling up my room with music. They even allow for room tuning, to suit the size of your room. They retail for $5000. If you would like to email me, I would be willing to share more info.

Look at the VMPS FF-3 Special Ribbon Edition (biamp only). They list for $8000 with the $900 Active crossover, but contact me for price. The level of hardware & construction quality are more inline with $25,000. the ribbon midrange was described by Tony Cordesman in Audio as a "new reference". The fanaticism in the active crossover is unknown by the competition. Hope you realize the level of final sound is dependant on many things besides the speakers. Cheers, & have fun searching.