At the risk of looking foolish, you may want to take a pair of headphones with you (or ask the store attendant for some). These can be plugged straight into the GNX3 which means you get to hear what the board really sounds like with out any coloration from amps.....just a thought !

You may also be able to get which ever unit you decide on for a couple of bucks cheaper by quoting one or two "online" prices at the sales guy, may be worth a try. Worked for a friend of mine here in Iowa !