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

My friend has an older rotel 5 channel power amp that he used to use with a rotel home theater preamp for a home theater.  Now he has a modern marantz home theater receiver that handles the home theater.  His new house has 8 in wall speakers distributed throughout the house.  He has a sonance speaker distribution box.  I advised him to use the rotel power amp to drive the speakers in the sonance box, using the pre-outs from the Marantz.  The current set up can only make use of 2 channels, due to the 2 pre-outs from the marantz, and thus, 3 of the channels in the Rotel power amp are going unused.  I'd prefer to put one pair of in walls at least on its own channels in the rotel, and minimize the quantity of speakers in the sonance box.

any thoughts?

Here is an option that is very simple to use 4 channels of the Rotel.

(Example only, quality should be same as interconnects used.) Use this type of Y adapter on each (L&R) of the SR5006’s main pre-outs.

This gives you 2 pair of stereo RCA outputs with a female connection. That way, you can use normal interconnects for everything. (The splitter box from the link in your post would work also, just using 2 of its 4 outputs.) Use one of the pairs for 2 channels on the Rotel to the SS6 like the current setup. Then connect the other pair to the input of a passive volume control,

cheap passive VC -

better passive VC - only one input would be used

with the passive VC output driving 2 more channels of the Rotel to the outdoor speakers. Indoor speakers will play as they do now, but outdoor speakers will be able to play louder due to the increase in available power not being connected to the SS6. The main volume on the SR5006 will still affect all speakers, but the passive VC on the outdoor speakers can be turned down or completely off allowing a desired volume inside. Keep in mind that the passive VC only attenuates, so maximum volume of outdoors will still be determined by the SR5006 volume control. No doubt the outdoor speakers will be able to play as loud or louder than they do now with a given indoor volume, but more important, this solves the problem to turn outdoor down or off.

Now to try and use that 5th channel on the Rotel gets a little more complex. You would need the splitter box from your link, 2 passive VC’s, and a stereo to mono converter like this,

I do not advise using a simple Y adapter to convert stereo to mono. See previous post.

I would definitely use 4 channels of the Rotel as this creates more flexibility between indoor and outdoor speakers, but not sure about trying to use that 5th channel. Is there a major problem with volumes between the indoor speakers? Something too loud, not loud enough? And if so, what?

TLS49, this looks like a very sound plan.  I will be happy to walk my friend through this!  Thank you both for the input.  I will be sure to tell what he ends up doing.
I was typing while you posted, but here is some additional input. Sounds like you have a solid direction in which to go.

My original post :

I agree that a resistive stereo to mono adapter is better than a y cable, although I find that in most situations the y cables are fine for this type of application. The one suggested should be fine.
And y cables can certainly be used to split out the signal into two signals.

I suggested using zone 2 because it can be independent of the main output. However, to use it you will need analog outs from the Apple TV, which I do not think it has. So, zone 2 is out if the source does not have analog outs.

So, that leaves the stereo pre-outs with volume controls(s) and Y cables and maybe a stereo mono converter. Several small parts, but it should work.

My guess is that the Rotel with handle a 4 ohm load (assuming that is what the SS-6 presents in Protect mode), but you need to check that first. Do you know the model?

If the Rotel handles 4 ohms, before going much further I would suggest hooking up the the Rotel to the 5006, and feeding that into the SS-6 with all the speakers connected. That will give you an idea of whether you have enough power to drive everything and whether you will need additional volume controls for different rooms and for outside.