Enjoy the audition, both of those speaker lines are well regarded. Just make sure that you bring your own test discs with you, and bring stuff that you're familiar with and that represents how you'll actually use those speakers. The last thing you want to do is listen to a piece of music for the first time in a demo room, since in that scenario you're basically evaluating the recording rather than the speaker itself. Dealers know which discs highlight a particular speaker's strengths, but if their demo discs don't represent what you like to listen to, then it's not nearly as relevant.

Also, take your time. Even if you really like something tomorrow, there are plenty of other speakers out there that you might like as much or better. Keep in mind your budget and stick to it. If you're planning for a multichannel setup, then you should also listen to the center and surround speakers as well, and check for how they match with the mains. With multichannel, you don't have to buy the whole thing at once. It's perfectly fine to add on incrementally.

And I wouldn't necessarily narrow down to floorstanders from the get go. When I began evaluating speakers a few years ago, I also initially listened to floorstanders, but as I went along I noticed that most of the floorstanders in my price range ($1,000 and below) had problems with cabinet resonance and problems with overall tonal balance. The equivalent standmounts typically did not have those same issues, and at the same time had better imaging, overall balance, and midrange coherency. The floorstanders have advantages in the bass extension, but the standmounts are typically better in other areas.

Since speakers tend to sound different from room to room, what you should really do tomorrow is pick out which speakers you like best out of the ones that are in that particular dealer's demo room. You should try and do follow up listenings at other dealers and see if your initial preference holds up (and it also allows you to do additional A/B comparisons with other speakers). Once you've narrowed down your list, make sure that you do a demo at home before put down any money on the speakers. Most higher end dealers will let you borrow the demo models that you're interested in, and ideally you would do the final comparison at home with your components. Room acoustics play a huge part in what you hear, and how speakers react to your room might be very different than how they reacted to the dealer's demo room.