Hi, and welcome to the forum!
Anymore, I'd have to research the general differences just like you, but hopefully someone else here knows the answers for you. At least back about six years ago when I bought my first Pioneer, the Elites had better power circuitry - but I don't know anymore. I wish that Pioneer's website would let you compare Elite and non-Elite models, but I can't see a way to do it...that would make it too easy.
From looking at their site, I noticed some differences:
- The 1021 has an integral power cord, but the 51 has a detachable cord
- The 51 includes 12V triggers (for a projector or the like, but it won't help with amplifiers because it doesn't have pre-amp outputs for anything but the sub)
- The 51 has an RS-232 connection, but that's more for custom installers
- The 51 has one more HDMI input (6 versus 5, including one on the front panel)
- The description for the 51 says that it has a digital audio output, but I can't see it - maybe it's on the front panel under the cover
VSX-1021
VSX-51