Integrated or separates?

INtegrated is good for your budget. US$1000 can get a decent used solidstate integrated amp with accepable power.

Copland CSA28 is a good choice in the range.

check out the denon pma-2000ivr at www.usa.denon.com
retails for $1200 80 watts per side 160 watts into 4 ohms.
puts out 120 amps of current.

Rotel electronics will match well the B&W 600 series. The 604's can also benefit from stuff further up the audio chain.

I would probably go with an integrated with a $1000 budget.
On the used market for separates, one thing you could look for is a older Conrad Johnson PV-10AL tube preamp or PF-1L or PF-2L solid state preamp. They are all around $500. For an amp around $500 either McCormick or a Conrad Johnson MF2100 or Sonographe SA250

A piece that really impressed me at CES was the Unison Research Unico integrated. 80wpc for $1300 brand new. It utilizes a tubed preamp section with two 6922s and a solid state output section. Very musical and it sounded great through Triangle Celius. I've seen used ones here for about $1000.