7125 = made in USA by ATI for Outlaw
5000 = made in China by ???

You already know about the difference in number of channels (2 less for the 5000) and difference in price (5000 is 60% of the price of a 7125).
I haven't heard either. Audition both and return the one you don't want. You're only responsible for the original shipping charge on the one you return.

My concern would be the noise floor difference. S/N specs aren't listed in the 5000 product page. I find it odd that S/N is listed for all the other amps they sell, but not this one (not in the product page or in the manual).

Best,