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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Bottom line, the fewer variables in your audition, the better.  If you can't audition it in your own home with your own preamp, speakers, and other peripherals in your own room, you're not going to be able to draw a reliable conclusion about how it sounds versus your existing amp. 

Bringing your preamp to his place will be better than listening to it with his gear, but it's still not enough info to make a solid decision about buying it. Not when we're in this price range, anyway. 
You should take the preamp home for a few days at least. No question. The real understanding of a piece of gear is listening the music after you stop listening to the gear. Then your subconscious forms an impression of the gestalt and you figure out if it moved your system forward or just made it different. .

My audio guy delivers and hooks the equipment up.
Problem is that he’s over an hour away in NYC, And because of my eye sight I can’t just jump in a car and return something- I can't drive anymore, I'm pushing my wife to take me to the city tomorrow. I don’t want to do it, but if I he won’t let me demo it at home I’ll have to be dastardly and buy it online from Audio Advisor or Music Direct if I like what I hear in the showroom. I really don’t like doing that to a dealer, but I’ll try to get him to put a hold on one of my cards so that I can do as you suggest and try it at home. HR from S-phile wrote that my preamp is very close to the Rogue RP-7 preamp, which he sells. He wasn’t crazy about the idea of having me bring my preamp because he has to move equipment and re-route cables, so there is no way he’ll say okay to me bringing in my cables.
Where do you live? Talk to John at audio connection in Verona NJ  I think he carries Bryston.