You're doing 5.1.2 on vintage equipment?

Buy enough speakers and you can do x.y.z

Can you? Doesn't the receiver have to know how to decode it?

It's absolutely possible to do whatever amount of channels you want, just buy enough amplifiers. You may need other equipment to "decode", but it's easily possible to get a media PC with 7.1 analog audio outputs, or more if you really wanted to do it for whatever purpose you need. None of this is really impossible, it just takes money.

> but the speakers should still sound perfect

speakers are wear items

I have a set of 1970s Sansui speakers that are still going strong. Nothing wrong with them. I use them every day, all day long, and have for decades.