Can I rig a home theater amp to run in wall speakers?

That is hard to say, though I would guess the outdoor speakers will need more amplifier juice, by nature of them being outside.  

Looks like they may not be summing speakers, he sent a photo and 3 pairs are connected as usual, but one line speaker only is connected to one channel. 

Thank you for the help!  

Outdoor speakers would be my guess as well. On the SS6, 3 positions are connected normal, L&R. Then 2 positions, hallway and kitchen, have only one channel connected. Correct?

I do have a couple of ideas, but really need to know the model number of the Marantz to know it's capabilities.

Just heard back from my friend.  It's the Marantz SR5006.

That Marantz has Zone 2 output, as long as you are using 5.1, not 7.1. You can use Zone 2 pre-outs to feed the Rotel to drive the whole house speakers. You can connect all the speakers to the SS-6 and the Rotel will probably have enough power to drive them, although I would check to see if it can handle the 5 ohm load from the SS-6. In-wall and outdoor speakers are usually pretty efficient so the Rotel should be OK if it has 100W output. You will probably need analog inputs to use Zone 2.  Also, check to see if the speakers are all 8 ohm. That many 4 ohm speakers would definitely be a problem

You can certainly use a simple RCA splitter to separate the signal in order to use 4 channels of the Rotel. There can be some minor impedance issues between the Marantz and the Rotel doing that, but the effect is pretty low and should not be an issue for whole house speakers.

The biggest problem will be volume control. You are almost certainty going to want to be able to change volume for different rooms. You could use impedance balanced speaker selector boxes like the Niles SSVC-6. Make sure such a box has impedance matching. For example, the Monoprice ones do not, I believe.

So, I would check the speaker impedances, the impedance the Rotel will handle and think about volume control.

Thanks Mark, and I have taken a look at the manual. Hopefully I can clarify some of the info provided by "dtc".

Zone 2 - When using Zone 2 speaker output, 7.1 is not an option for HT, however when only using Zone 2 pre-outs, you can do 7.1 HT. These Zone 2 pre-outs can drive 2 channels of the Rotel amp, but not directly. A passive VC will need to be inserted between the Zone 2 pre-outs and the Rotel amp. The manual implies that the Zone 2 pre-out is a fixed output, so depending on its level, it could overdrive the amp. It is true that Zone 2 will only play sources from analog inputs or the tuner. Any sources from HDMI or digital inputs are not available for Zone 2.

Using the stereo (L&R) preout - I believe this is the current setup. It will be necessary to select stereo only on the SR5006, no surround. Then the main VC will affect the volume of all speakers. "Is there a way to disable the speakers on the Marantz HT Receiver while the pre-outs send signal to the other speakers?" Yes, assuming there are no speakers connected to the speaker B outputs. The "Speaker A/B" switch on the remote will toggle, (A) - (B) - (A+B), then back to A. Set this to "B", then the HT main speakers will not play. Since stereo only was selected on the receiver, center and surrounds will not be playing as well. Also, if stereo only is not selected, these preouts will only output the L&R of a 5.1 signal, and likely sound poor on the in-wall speakers .

Trying to use more than 2 channels of the Rotel amp - possible, but a few ways to do this. Rather than list all the scenarios, is it possible to get a little info on what sources are used for the distributed audio, analog, digital, or both? For example, 2 channels in addition to how things are currently setup could be driven from Zone 2 pre-outs as described above, but those speakers would only play an analog source. RCA splitters could also be used, but depending on the arrangement, additional devices may be necessary.