Monoblocks usually aren't necessary and the needs, performance wise, be met with a stereo amp. Only when you have one speaker do you need a monobloc. While the monobloc offers an infinite channel separation, good solid-state stereo amps can have 90db separations. 20db can produce a believable stereo performance. So to have monoblocs many parts costs double, and all things being equal, offers a negligable gain in performance, at least in comparison to what could have been done if the designer reinvested into the circuit in a stereo setup. Alot of stereo amps share a power supply, and the rest is more or less mono, and with good PSRR (power supply rejection ratio's) crosstalk should me minimal. Biamping, on the other hand, can offer very good results cutting down on intermodulation distortion and increasing dynamics. Its real forte is with electronic equalization; however, it can be done with both amps running full range with filtering through the passive networks and get a respectable performance increase. If I were to explore one it would obviously be the latter, unless you're pushing the ultimate in resolution threshold where a well designed monoblock will have better performance, but for $$ range you're in I'd still lean for the biamp. It does depend on the specifics of the deal you find.
