@ymc226
For surround setup (HT) you will have to connect everything to your McIntosh MX135 av preamp processor (pre pro).
I wouldn’t connect the optical digital out of your TV to the MX135 as it won’t sound good at all. I’m aware that your MX135 does not have HDMI inputs.
To get the best surround sound possible connect your bluray/dvd player using coax digital audio (spdif) cable to your MX135. I’m sure your MX135 has coax digital audio & optical digital inputs. And you will still have to run HDMI from your bluray player to your TV for video only. Or
If your bluray player, such as that of the Oppo bluray player, has multi-channel analog audio out (5.1 or 7.1) you can connect your bluray player both using coax digital audio out of the bluray player to the MX135 for outputting lossy Dolby Digital & lossy DTS surround sound formats found on DVD movie discs since your MX135 supports those lossy formats, and also connect the multi-channel analog audio out (5.1 or 7.1) of the bluray player to your MX135 and set your MX135 in analog bypass mode thus bypassing its DSP and other digital processings. And use this multi-channel analog audio connection to output those lossless DTS-HD Master Audio & Dolby True-HD surround sound formats found on bluray discs. And on your bluray player turn off the HDMI audio out on your bluray player when using this multi-channel analog audio output of your bluray player.
Cause your MX135 does not support those lossless DTS HD MA & Dolby True-HD formats from bluray discs. If you use coax digital audio cable to the MX135, your MX135 will downgrade these lossless formats to lossy Dolby Digital & lossy DTS. These lossless DTS HD MA & Dolby True HD can only be transmitted to their fullest bandwiths using HDMI or multi-channel analog audio (7.1). If you use coax digital audio or optical digital these lossless formats (DTS HD MA & Dolby True HD) found on bluray discs will be downgraded to their lossy counterparts (DD or DTS).
For the multi-channel analog audio connection you must use RCA analog audio cables.
For your cable TV box, run HDMI to your TV for video only and run a separate coax digital audio or optical digital to your MX135 for audio only. If your cable TV box has a coax digital audio output use that instead of optical digital. Generally coax digital audio connection will result in better sound than optical digital. But if your cable TV box had only optical digital out then use the optical digital to your MX135 for audio only.
Fyi, all audio formats coming out of cable TV box would be all lossy Dolby Digital or lossy DTS anyway, so either coax digital audio or optical digital will do it. And besides, none of cable TV box would have multi-channel analog audio outputs like those found on some bluray players such as that of the Oppo.
Hope this helps.