Can McIntosh 135 be used with non-McIntosh amp?

Yes the MX135 can be used with amp as long as you don't want to use the McIntosh 6 channel single cable ambilical.
You can use the six channel analog outs just not the single computer looking connector. As far as amps, McIntosh would be a nice match but Ayre, Audio Research, Bryston, to name a few that would work nicely. I owned a MX135 and It is very nice piece and for someone to give you one is a very very nice gift. Enjoy!!

Thanks Theo - just what I needed to know. The 25 conductor cable labeled "Multi Channel Amp" had me intimidated. As long as I can use the analog outs without any issues, I should be ok. Thanks again!

Yes you'll be ok with the standard analog outs. Pick you favorite style of amp ( not usually a mini box but that's up to you) and you'll be off to the races.