Quandary

Wait until they or someone else can offer you the exact amp he’s recommended. It will sound different than the one’s he’s actually recommended. Find other opportunities to listen to the amp he’s suggested in home or in store or at another customer location.

Jetter is correct. This is strictly a class A pass amp. It will sound very different from your benchmark. For better or worse will be subjective. Good luck. 

Most shops that do offer home demonstration will do so only with customers they are familiar and can trust.  They will help you load it in your car, but beyond that, it would be a big imposition to expect them to set up in your home on the hope of a sale.  The crediting to your purchase price the fee for the demonstration is what I expected.  The question is whether $300 is reasonable.  If they give you enough time to seriously audition the amp, I think it is reasonable.  Ideally, they would leave it for a few days and return to pick it up.  
 Pass makes some very nice sounding amps, and the smaller amp you are considering will probably sound very similar to the higher powered amp if your speakers are efficient and the two amps have similar topology and are comparable in quality level.  I’ve even heard comparisons where the lower-powered amp by a particular manufacturer sounded better than its more powerful sibling.

@rvpiano not talking you into this deal. But the XA30.8 is a great amp and with your tube preamp you will have fatigue free listening. If you can get a hand setting it up, buy used. The XA25 should be great as well. I respect benchmark but am not a fan of their house sound. It’s a personal choice.
 

The XA30.8 operating temperature is about 104-107 degrees Fahrenheit. If heat is a consideration. Other than that I can’t think of any other drawbacks. Don’t worry about power cords. Whatever you’re using on benchmark should port over just fine. If not then the stock cable will hold you over as well.