Square peg round hole?

Cowmoozik, I've been driving Maggie 1.6 QR speakers with BC2s for the last few months and they drive a very difficult load between 1.8 - 4 ohm. Some people including Gilbert Yeung I believe have run them with Martin Logan CLS speakers. Anyhow, these can drive 4 ohm speaker systems, not with great authority but beautifully. If ballz to the wallz is what your looking for than you should consider an efficient speaker of 8 ohms or more with a high sensitivity rating, which incidentally I personally plan on trying.

Would Blue Circle BC2s be able to drive a pair of Kef 105.4s properly?

I don't know but "Cowmoozik" is one cool name.