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

" His new house has 8 in wall speakers distributed throughout the house."

8 mono speakers, 4 pair stereo. or 8 pair stereo? 

"using the pre-outs from the Marantz"

Stereo or A/V, and if A/V, main preout or zone 2 preout?

Any way to control volume of individual rooms?

"Do the RCA splitters have any major negative effect?"

I would be more concerned about the speaker distribution box. Some have as much as a 50% power loss. Do you know the model number of this box?

tls49,  thanks for the help!

he has 1 pair of outdoor speakers, 1 pair in living room, 1 pair in family room, a single speaker in kitchen, and a single speaker in a hallway (which is a low priority).

On the Marantz HT Receiver, he is using the main speaker outputs for his home theater, and then the stereo pre-outs to the Rotel amp.  Is there a better way to feed the Rotel here?  What is the A/V out?

no way to control volume in each zone

At this point, we are shooting for a minimally functional system!  I advised him that a great way to do this properly would be to purchase a Sonos Connect Amp to each pair of speakers for excellent control, but that is an expense he does not want to incur at the moment.  So, to use what he has will have to do for now.  Is there a way to disable the speakers on the Marantz HT Receiver while the pre-outs send signal to the other speakers? 

Hi Mark,

Happy to try and help. Retired now but worked in the A/V industry many years with experience in HT and distributed audio. I have some ideas but need more info to see if there is a way to use what he has and make it function correctly, safely, and be user friendly.

Do you know if the single speakers are what is called a summing speaker, plays both channels with L&R connection on the single speaker? One way to find out is look at the selector box to see if that position has both channels connected, assuming a 6-way selector box. If it's a 4-way box then he may have L speaker in one location and the R speaker in the other. Model number of the selector box would be great or does it have knobs and switches or just switches and how many, 4 or 6?

Can you get me the model number of the Marantz? Should be close to the name on front, in small print.

I know I'm asking for detailed info, but without it is like shooting at a target blindfolded. Get what you can and we will kept working toward a solution.

Just found out it's a Sonance SS6, waiting on the Marantz model number 

OK, with the SS6, I'll assume the single speakers are summing speakers as I described above, and he is using 5 of the push button switches, one for each location, 3 rooms, hallway, and outdoors. When playing multiple locations, which one could use a little more volume?