Boulder / Halcro are great SS amps .
That is a big sound speaker by the way although i never heard one
6 12 inchers per side

The min imp is quite high 5 ohms and a reasonable eff, a powerfull tube might work also
What i found on their site :
SPECIFICATIONS
Frequency response is from -4dB @ 13 Hz to well beyond 24,000 Hz.
Efficiency is 88dB.
Impedance is 7 Ohms, nominal.
Minimum impedance is 5 Ohms.
Tweeter: 1″ cloth dome.
Mid-bass: Twelve 6″ double-magnet driver, with a 3″ voice coil diameter.
Bass: Six 12” woofers loaded in parallel chambers in pressure driven configuration.