There should be a button that changes the input of the MX121 on the tv, then you can access the test tones etc there to do your set up. I have an MX120 and there’s a button on the face that says a setup. You have to connect the HDMI to the tv properly. Download the manual if you don’t have it.
McIntosh MX121 Test Tones?
We have an audio system here that employs an Oppo BDP-103 as its DAC. We also have an MX121 that we wish to use as our multichannel (MC) analog preamp. This being the case, we have RCA cables running from the rear of the Oppo to the 7.1 CH INPUT jacks found on the rear of the MX121 ... and as an aside, the audio being used for testing is also known to include proper 5.1 audio data.
On the output side of the setup in question, we've connected a power amp (and a speaker) to all of the applicable RCA analog output jacks found in the UNBALANCED PRE OUT section of RCA output jacks: FL, FR, C, SW1, SL & SR. All of the amplifiers, save the center (C) power amp are working and, additionally, their front panel meters are responding to their audio signals.
As we don't seem to have a center (C) signal, I phoned McIntosh Labs to ask about this problem. The fellow that I spoke to seemed to be very busy, so he quickly said that I should start troubleshooting the issue by employing the test tones that can be accessed via the manual setup menus within the MX121.
If anyone has done this kind of troubleshooting, I'd appreciate some help on how to access said test tones.
Thank you for any help with this.