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

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. 

If, in fact, one of the speakers is truly mono, then you might want to think about making everything mono.    Wall and ceiling speakers and outdoor speakers seldom benefit from being stereo and mono is often better since there is seldom a "sweet spot". You can do this with simple Y cables - not elegant and I would not do it for critical listening, but it is often a good option for whole house music.

Thanks guys.  The source is an Apple TV via HDMI to the Marantz.  The Apple TV serves up a large collection of music on hard drive.  My friend is not an audiophile, he just likes music.  He is not even a gear enthusiast, nor one to obsess over the quality.  Of course, he appreciates nice sound, but there you have it.

TLS49, I think we are on the right track with the stereo output, taking advantage of the HDMI input on the Marantz.  So, he chooses stereo mode, sets the speakers to speakers B only, and his in-wall system is doing its job.  Sounds great.  

This is a relatively temporary band aid situation.  I think a stack of Sonos Connect Amps (or similar) would serve him better, but this solution may remain for a while, so we'd like to get the most out of it.

I really like the idea of using all 5 amp channels on the Rotel.  It just makes sense to have a speaker than can get its own 100 watt channel to take advantage of that, as well as to reduce the load and loss on the sonance box.  I think the outdoor pair can get 2 Rotel channels, perhaps the kitchen gets one (in mono?) and the sonance box gets a pair, now with only 2 pairs of speakers, reducing the load!

What do you think of this product?
https://www.amazon.com/HDE-Composite-Video-Powered-Splitter/dp/B009NK550I/ref=sr_1_3?s=electronics&a...

How do we get the kitchen in mono?  One of these?
https://www.amazon.com/Cables-Go-03161-Stereo-Y-Cable/dp/B0002J1KVM/ref=sr_1_5?s=electronics&ie=...

Ah heck.  I just realized there is a flaw in that plan.  He'd need to be able to turn off the outdoor speakers.  Cant be jamming in the living room, not using the outside area, and pissing off the neighbors.

Ok, please advise.

thanks!

dtc, I agree with the idea of a mono due to no "sweet spot", however, IMHO, I would not just use a simple "Y" cable on the L&R pre-outs of the SR5006, main or Zone 2. This just shorts the 2 channels together, and may cause adverse effects. It would be best to use some type of a stereo to mono converter, even something as simple as a "Y" with resistors inline on the signal connections.