Used Processor for Cheap as Dirt Magnepan Theatre

As a lifelong Magneplanar fan, I would like to experiment with their home theatre speakers to surround a new desk in my office.

For front left and front right I will use a vintage pair of Magnepans, probably MG IBs or taller, but nothing less than 5 feet tall.

I may not ever watch an entire movie, play at loud volumes or use a subwoofer of any kind.

But I would like to create a more immersive, non fatiguing environment for watching televison, multi media web surfing, background music etc.

For each channel, perhaps a Behringer A500, whose virtues as a dirt cheap monoblock have been well praised in another thread.

Can someone help me complete the idea with the best bargain for a surround sound processor on the used market?

Or any other ideas for a system/application of this kind?

Thanks for any ideas.