Quandary

It’s telling that you were satisfied with your system, and he made the suggestion of an audition, not you. My dealer would never charge a fee for me to hear a component that he is trying to sell. Even if you can get by that, you are still not going to know after the audition because it’s not the same component.  You might get some approximation of the pass house sound but the component you’re going to audition will likely sound very different in your system than what he is actually trying to sell you. At a minimum, I would insist that you audition the particular component that is under consideration. 

@OP -  you should find a dealer who will allow you a home audition of the amp for free. Offering to waive the $300 cost if you purchase is a clever sales tactic to subtly pressure you into buying in order to recoup your $300 outlay. In addition, it's ridiculous that he wants to charge to demo an amp which is not the actual model you would be buying. The Pass class A amps have a common sound character but they don't sound identical. However, as regards the comparisons , if you find your Benchmark slightly sterile/mechanical sounding, you will love the Pass. But you would need to hear exactly what you would be contemplating buying. The amps sound good from cold take an hour to warm up and about two hours to sound at their absolute best.

This sounds similar to a senior phone scam. 

About the Pass 30.8: Why not buy it here, used, for $4500 and resell it if you don't like it? The amp is $7.2k new, so you won't lose very much on resale, especially if you bargain a little. 

@rvpiano OK, a little perspective.  Somebody wants to sell you something he doesn't have.  (Alarm bell number one.)  He says he's got a pair of monoblocks at twice the power of the stereo amp he doesn't have and is willing to set those up for you for 300 bucks, which would be credited toward the purchase price of the stereo amp he doesn't have.  (Alarm bell number two.)  Monoblocks at twice the power of a stereo amp from the same manufacturer are very likely going to sound, at least different, and probably better, smoother or more sophisticated than a stereo amp at half the power.  (Alarm bell number three.)  Is this guy's name Trump, by any chance?

Sounds, to me, like you've got the upgrade itch!

Why not tell this guy to get the amp he says he wants to sell you and let you know when he can come by and set that up for an in-home demo, AND FOR A LOT LESS THAN 300 BUCKS!  REALLY!  How much time does it take to swap out two stereo amps?  Whatever in-home demo customer service charge the two of you might agree on should, of course, be credited toward the purchase price of this amp he's so sure you'll like better than yours.  Also, you should insist on at least a couple weeks for this in-home demo time or whatever gives you a good 20 or 30 hours of serious seat-time time with this new amp.  The "deal" he's pitching to you now sounds, to me, like he's really trying to sell you those monoblocks which, I'll bet, are used or demo equipment.

Let conscious be your guide and good luck!