Quandary

The only caveat is that I won’t be hearing the exact same thing that I’m buying. 

yes, that's a big caveat

Right now the Pass seems a little “overwhelming” and not quite as detailed as the Benchmark on some things. I have to keep the volume knob way down. However it certainly fills in a lot of gaps in volume that the Benchmark lacks.
I suppose that was to be expected.  

OK, the $300 is invested.

If you would decide to go ahead with purchasing the Pass amp maybe (if you haven't already) it's a good time to discuss in the unlikely event that you feel the single chassis Pass is not a significant enough improvement to warrant the expense, the method that this would be handled.

  LP

If you have to turn the volume way down then it is a gain mismatch with the preamp that you are using!

The Benchmark amp has three levels of gain via a switch on the rear panel. The highest gain of the Benchmark is 22db. The standard gain on the Pass is 26 db. Quite a difference when dealing with the same source/preamp; more than 3db of a difference. This should not be an issue with the CJ PV11. For the same in room volume level, you will be lowering the volume control on the preamp...no surprise here. The PV11 is phase inverting, meaning somewhere in the system you need to invert phase. Unless there is a phase reversal switch somewhere, this is usually accomplished with the speaker cables at either the amp end or the speaker end. At one end only, the positive wire gets connected to the negative connection of the amp/speaker, for each channel. Not meaning to confuse you rv, just some insight. My best, MrD.