Bring my own preamp to an amp demo?


I'm going tomorrow to demo a Bryston 4B3. I have a PrimaLuna Evo 300 preamp and Harbeth 30.2 XD speakers. The dealer suggested that I use a similarly priced preamp that he sells, but if I want to hear the amp with my specific preamp and the speakers I own (which he sells, and I bought from him) I need to drop it off when he opens and come back later because he has other appointments booked and needs time to connect my PL preamp, and maybe (I'm guessing) get it warmed up. I'm also going to listen to a BAT VK-56SE, and he suggested I keep an open mind and listen to an Einstein Integrated amp and thinking about selling my PL Evo 300 preamp. He wants me to have an open mind, and said he has a lot of customers that like and bought the Einstein with Harbeths. He also has an Audio Note amp demo for me to listen to as well. He's not a fan of PL, but is happy to work with me.
Bring my preamp or not?
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They offered to lend me a preamp for a weekend when I picked up the Maggies I purchased there. I haven't taken them it yet as I wanted to wait for the Maggie's to break in.  I'll be talking to John soon about preamps.
I can't do a weekend loan, my traveling situation demands a week. I see he has a 30 day return policy.
Everything I've heard about John at Audio Connection makes me believe that if I lived in the area (I used to) I'd want to start a relationship with that store. Not only for this purchase, but for future purchases and for his advice and support of the gear. I have bought locally and I'm not crazy about my local store; they don't get back to me, they seem to have other fish to fry (bigger clients). They don't understand that this is a longer term relationship.