@tomiiv30
For your B&W 683 S2 speakers you can use your Marantz AV8805 and your Mac MC8207 seven-channel amp for both stereo and HT imo until you upgrade your front speakers for stereo listening, then you can start looking for a dedicated stereo preamp with HT bypass feature and a better stereo or monoblock amps for your front speakers. But until then you are good with what you have.
For your B&W 683 S2 speakers you can use your Marantz AV8805 and your Mac MC8207 seven-channel amp for both stereo and HT imo until you upgrade your front speakers for stereo listening, then you can start looking for a dedicated stereo preamp with HT bypass feature and a better stereo or monoblock amps for your front speakers. But until then you are good with what you have.