Mcintosh MA-7900 home theater bypass with subs - not doable?

I don’t own the 7900 but you can do it with an external crossover. You could pull the bars in the back that connect the preamp section to the amp and insert it there. Out of the preamp to the crossover then back into the amp input. From the crossover then out to the subs and from the home theater processor into the subs at the same time. 
 

An active crossover like the JL audio CR1 will take both a 2ch preamp and home theater LFE at the same time. Something like a mini dsp might work too but I have not used one before. 

I think the preamp outputs will work. Have you thought about high level inputs to the subs and bypass EQ when listening in stereo?

I ended up not trying it but I think the answer was to use the pre outs.

Did this ever get resolved? If so how as I have a 7900 coming and hope to do the same….? Thank you

Equalizer Bypass

Press the Front Panel EQ BYPASS Push-button to remove the MA7900 Equalizer Control Circuitry from the signal path for the currently selected Input Source. The LED above the EQ BYPASS Push-button will il- luminate. Refer to figure 50. The MA7900 remembers for each selected Input whether the Equalizer Control Circuitry is deactivated. To reactivate the Equalizer Control Circuitry for the currently selected Input Source press the EQ BYPASS Push-button.

Note: 1. The audio signal present at the RECORD OUT Jacks is unaffected by the Tone Circuitry.

2. The EQ BYPASS can also be accessed by the TRIM Function, refer to page 24.

AND, I also found this:

• PassThru Mode: The Automatic PassThru Mode allows the MA7900 to become part of a Multichannel Sound System for DVD-Audio, SACD and Home Theater Movies.

AND, please see page 19, etc. for more info:

Passthru

The MA7900 can be part of a Multichannel Sound System for SACD, DVD-Audio and Home Theater. The Right and Left FRONT Channels from an Audio/ Video Control Center or Surround Decoder can “Passthru” the Preamplifier Circuitry of the MA7900, and then on to the Power Amplifier Circuitry of the MA7900. The Setup Mode allows the activation of the Passthru Mode and the selection of the specified MA7900 Input Source. In the example below,

the Right and Left Front Channels from the Audio/ Video Control Center will be connected to the SRVR (Server) Input Jacks on the MA7900. Refer to page 10 for additional connection information.

Notes: 1. The Phono Input Connectors and Digital Input Connectors are not assignable as a Passthru Input.

2. If the Balanced Input Connectors are already reassigned to a given Input, they will not appear in the list of available Inputs for the Passthru Mode.

3. When one of the RCA Inputs is selected as a Passthru Input, it is advisable to remove it from the list of available Inputs by switching it Off. Refer to “Source Inputs Reassignment” starting on page 18.

1. Press and hold the INPUT CONTROL until the Front Panel Display indicates the Setup Mode is active. Then rotate the INPUT CONTROL and select the Setup Menu item “SETUP: PASSTHRU, Source: OFF”. Refer to figure 15.

Figure 15

2. Rotate the VOLUME Control until “SETUP: PASSTHRU, Source: SRVR<RCA> appears on the....please see the manual for more info.

The above says "The Right and Left FRONT Channels from an Audio/ Video Control Center or Surround Decoder can “Passthru” the Preamplifier Circuitry of the MA7900, and then on to the Power Amplifier Circuitry of the MA7900". THIS MIGHT BE YOUR PROBLEM.  I DO NOT KNOW.

As several others have posted above, please call McIntosh direct for assistance or a McIntosh retailer.