I'm not sure I follow exactly how you have it hooked up now, but you'd be better off removing the switch box from your system. You don't need it. If you want to use the McIntosh for your front power and Stereo, all you need to do is to connect your Yamaha Front pre-outs to one of your un-used inputs on the Mac (eg Tape in). Then when you want to play HT Mode, you simply select that input on your Mac.
The first time you do this you need to calibrate your speaker outputs. Select the 12 oclock position on your Mac volume control, or some other easily remembered position. Then your receiver volume control will drive the power amp in the Mac. It will also drive your subwoofer through the Mac pre-out. The only problem with this is you won't be getting LFE from the sub outputs - but it doesn't sound like you're getting that anyway.
I have used this set up and it works beautifully - and this has been discussed many times in other threads. Another 'goner explained it to me.
The other advantage is you don't decay your 2 Channel Mac performance with a cheap switch in the chain.
good luck . . .
The first time you do this you need to calibrate your speaker outputs. Select the 12 oclock position on your Mac volume control, or some other easily remembered position. Then your receiver volume control will drive the power amp in the Mac. It will also drive your subwoofer through the Mac pre-out. The only problem with this is you won't be getting LFE from the sub outputs - but it doesn't sound like you're getting that anyway.
I have used this set up and it works beautifully - and this has been discussed many times in other threads. Another 'goner explained it to me.
The other advantage is you don't decay your 2 Channel Mac performance with a cheap switch in the chain.
good luck . . .