My understanding is that the Lexicon RX-7 is pretty much the same amp as the ATI AT2007. With that said, get the ATI with warranty.
ATI supposedly does some OEM work for Lexicon among a number of other manufacturers. I've never seen what the different specifications Lexicon has for their requirements much less any other manufacturer. I agree with Willand that if you can get the ATI with the warranty, that's the way I'd suggest too. Make sure that the warranty is transferrable with the ATI. That's the only red flag for me,
Your wife may like the looks of the Lexicon better. The ATI's are truly a plain industrial design.