Bridging my power amp

Not familiar with the BAT's but...

Bridging usually quadruples in power. Paralleling doubles output and makes driving lower impedance speakers easier. Since the BAT is already balanced (differential), one of the reasons to bridge is moot.

Thiel CS6's are low impedance (under 4 ohms) through most of the bandwidth but that's partially negated by even phase response. so as not to be a "tough load". Even so, they would respond well to 150's, which is rated for 4 ohms, especially at higher SPL's.

BAT does offer upgrading the 75 to the monoblock 150, which seems like the safest route.

Bridging an amp doubles the avaliable voltage that can be supplied to the speaker but does not increase the current. If driving high impedance speakers, then the power is x4. If driving low impedance speakers and you are already going up to the amps current limit, then you won't get anymore power than non-bridged amplifier.