Jamie, as BMXTRIX said, some specs, especially power ratings on older equipment tend to be smoke & mirrors from some OEMS; and IMHO the cheaper the equipment was initially, the more bogus the numbers are. For example the manual for the SB-SL701s has input power at 200W (music) which for most folks is a "non" spec and really just a marketing number to influence sales. Power ratings need definition parameters for them to be believed. Even the Frequency range published, although with parameters, is strange. => 33Hz ~ 22kHz (-16dB) and 41Hz ~ 20kHz (-10dB) most use deviations like +/- 3dB at most. Better speakers use even tighter numbers.
Please answer all of the questions members here ask, as we are truly just trying to help you out. Without responses it makes the process that much harder.
As for the Sony buzzing, please define what's going on. Is it a 60 cycle hum? Typically most folks have "buzzing issues" related to grounding problems, or adjacent electrical equipment inducing noise onto the powerline. (Typically Refrigerators, Fluorescent Lights, pumps, fans, etc.) Start with only a single speaker connected, and a single source and try to plug it into a circuit without anything else. If it buzzes on radio (FM is probably better than AM) and a single speaker, then swap the speaker. If it doesn't buzz then it could be something connected to the STR-DG820. Add one device at a time until you find the one causing the issue.
Troubleshooting can be time consuming, but you need to be methodical and change only one parameter at a time. I get it you are on a Budget and being cost effective is admirable, but sometimes Free stuff just won't give you the results you are looking for.
I hope this is helpful.
