Well, first as a nitpick, they're not acronyms, they're just abbreviations (or technically initialisms). To be an acronym, it has to be pronounceable as a word, such as radar.
Now, I don't know what AVC stands for, it just seems to be a prefix for some Denon models. AVR is Audio Video Receiver, and AVP is Audio Video Preamp, basically the same as a receiver except the power amps. The selection of AVPs is fairly low in the market, but most higher end AVRs include preamp outputs, so you can still add your own amps, and not use the internal ones, if you prefer. It can be debated whether an AVP is higher quality than the same company's AVR with the same features, but that's an argument I'm not going to touch.
