RJM Music Technology, Inc. - Creators of the RG-16, Amp Gizmo and other MIDI switching systems
It is not cheap, but what you are looking to do is a lot more electronically complicated (read: expensive components and development) than most people realize. The good thing about this unit is that it supports four loops for the effects loop of the amp, and four independent ones to use wherever you want in your signal chain, plus it controls up to four channel switches and four function switches on your amp.
Now, having said that, effects loops are no place for pedals. Pedals operate at signal level, not preamp level, so you will be lowering the level before it goes to the power amp. You will get more noise, and cold, stiff power amp response. This is why people use rack multi-effects processors: they are designed for the job. So, absolutely use your favorite tone shaping pedals out front, and use rack gear for time-based effects.
I know you probably love that chorus or delay pedal you have, but I have come to realize they just aren't terribly useful. Live, no one in the audience is going to be able to tell the difference, and in a studio, you're recording dry and adding effects at mix. Through years of trial an error, I have come to realize a good live rig is a simple rig. That's why I've got one halfstack, one effects processor (G Major), a wah, a wireless, a tuner, and a MIDI controller.