What used amp should I pair with my newly acquired Monitor Audio GR60's?

Would like to spend under $500 or so. Currently using a Pioneer Elite VSX-52TX which has a broken 2nd zone binding post, so no bi-amping from it.

Looking to upgrade to a nice 2 channel. Should I be looking to try & bi-amp ? (or tri-amp? which you can do with these, but not at this price limit)

Any help appreciated.
Thanks.