The 2.7's have a nasty (2.4ohm at 160Hz)load, this together with whatever negative phase angle, could go even lower.
This is probably why the Bel Canto's Class D's lost out in the lower mids, as below 4ohms Class D's usually cannot double.
If you want the very best out of them I would look at solid state amps that can come close to doubling wattage for each halving of impedance, which means they can deliver good current.
IE:
8ohms 100watts
4ohms 200watts
2ohms 400watts
These would be solid state amps with BJT ( bi-polar not Mosfet) output stages, with nice hefty power supplies, in other words big heavy BJT amps.
Cheers George