Pass Labs 150.5 suitable?

Assuming that the speakers are truly a benign load as you indicated (meaning that their impedance does not dip down to very low values at any frequencies, and that they are not highly capacitive at any frequencies, such as electrostatic speakers would typically be, for example), 18 amps should be plenty.

18 amps into a purely resistive 8 ohm load corresponds to 2592 watts (18 x 18 x 8). So the short-term peak power that the amp can deliver would be limited by its voltage swing capability, which is spec'd at 50 volts. 50 volts into an 8 ohm resistive load corresponds to 312.5 watts (50 x 50/8). Some combination of thermal (heat dissipation) considerations, energy storage capability, design margin, and other factors reduce the long-term (continuous) rated power to the specified 150 watts.

Regards,
-- Al

I believe Pass Labs volt and amp specifications are specified as peak-to-peak, vs. some kind of short-term average power level.

So 50 volts p-p corresponds to 35.36 volts RMS, giving an "RMS" power rating of 156.25, so it's less a matter of design margin, etc. than just a different type of specification.

Good point, Auxetophone -- thanks. I suspect that what you are saying is correct, now that I think of it (except that I think you meant to say "peak" when you wrote "peak-to-peak" or "p-p").

So my reference to 2592 watts as being the limitation that current capability would impose on power delivery, were it not for voltage swing limitations, becomes:
(18 x 0.707) x (18 x 0.707) x 8 = 1296 watts.

So the basic conclusion that the X150.5's current capability should be sufficient for the described speaker load remains as stated.

Best regards,
-- Al

I agree that the X150.5 should have enough current - and yes, I did mean "peak" and not "peak-to-peak", which would have been 100V.