Are you using the Pioneer/C-1/M1.0 as pure stereo(?) ...or as the mains in an HT?
Anyone have any idea where i should set the volume level on the C-1. I dont want to over load the inputs on my Pioneer
As I read your post and understand the question, that is entirely up to you, which is completely subjective. Regardless of whether you're using this gear as a pure stereo or as the mains in an HT, nothing will be overloading the Pioneer regardless of settings; you are merely using it as the signal source for the C-1, as a DAC/decoder in particular. What you do with the signal after that does not affect it, whether it's turning it up or down on the C-1.
I have similar components to my Stereo/AV system but might run it slightly different. I use my receiver (Integra 7.6) as a DAC and multichannel processor (phantom center) as well. I also have a C-1 for my mains, but also use a C-2 preamp for my rears and my front and rears are bi-amped to their own subs, so use the 'sub off' mode. When I want to listen to pure stereo however, I have components plugged directly into the C-1 and the processor is not even in the chain -well, unless I'm using it as a DAC at that time or I'm in multichannel mode. If I'm using my Integra as a DAC like you are planning with your Pioneer, I generally keep the volume knob on the C-1 with the marking dot at 12 o clock
and use the volume function of the receiver which is nice cause it has a remote. ^_^ Ultimately though, for pure stereo listening, bypassing the receiver and plugging directly into the C-1 sounds better, but makes you have to use the volume knob on it and there ain't no remote for that!
If you are using this in multichannel, to be more specific in answering the question depends on how prominent you want your mains to be in relation to the other speakers, but you would use the receiver's built in level calibration tones (RTFM) to find the happy spot and take note of the position of the volume knob on the C-1 that correlates with volume levels to match the mains to the other speakers outputs, so you can get it back to that spot if you move it.
There is really no good reason to not have a bad ass stand alone stereo as your mains in a larger HT setup, other than cool points from the purists. The C-1 has many inputs, and only one of those has to be connected to the HT receiver...