I have (and love) the PSB Imagine B speakers; it is probably better to think of the PSB synchrony two bs as 4 ohm speakers (that's certainly true of the image b speakers as well). The PSB web site has the synchrony two b listed as 6 ohm nominal, 4 ohm minimum; sites like Crutchfield list them as 4 ohm speakers.
If you don't care about video, you could just buy a 2 channel amp or receiver. If you are looking for a stereo receiver, you could get any of these:
(1) The outlaw rr 2150; I'm using an outlaw 2150 (which does 160 watts into 4 ohms) to drive my PSB imagine b speakers and the combination works great. You can pick one up one "b" stock for $649. Looks great and sounds great.
(2) Harmon Kardon 3490 which runs around $350. There is a very positive review of it on this website.
(3) Marantz SR 4023; you can pick one up refurbished from accessories4less for $299 with a manufacturer's warranty:
Marantz Sr4023 80w X 2ch Ci Friendly Stereo Receiver | Accessories4less
A lot depends on what you want it for. For music only, these are good choices for a stereo receiver. If you are planning on using a computer as a source, then you should consider a receiver or an amp that has digital inputs. The HK 3490 has a digital, the Marantz does not, and the Outlaw has a usb input. Another alternative is the 9050 amp from Onkyo:
Amazon.com: Onkyo A-9050 Integrated Stereo Amplifier (Black): Electronics