I may be late to the table here but I believe one thing that does not get talked about when choosing an amp for a highly efficient set of speakers is damping factor. Choosing a normal solid state amp on efficient speakers will strangle them.
Judd Barber of Joulle Electra fame talked about damping factor that anything above around 8 and the amp will start to swallow up the bass notes - this is compounded with high efficiency.
Hence Croft makes it a great choice for your Altec speakers - it measures like a tube amp.