TOPIC: C-DSP 6x8 Input Gain & Noise Floor

Hello — Two related questions. I’ve seen these topics touched on and answered in slightly different ways, yet I’m not sure I quite understand the responses, so I’ll ask differently....
First, Porsche PCM 3.0 speaker leads are running directly into the high-level inputs of the C-DSP. I play 0dB test tones with volume level maxed on the head (let’s assume no distortion from the head for the moment), I get to about -10dB on the C-DSP input meter. -5dB test tones at max volume get to about -15dB on the input meter — seems to make sense. If I raise the input sliders to +12dB, I can just get the input meter to cross 0dB (presumably input clipping).
I don’t listen to music recorded close to 0dB, so I think I’m leaving unnecessary input headroom with my current setup, and causing me to crank the amp gains too much leading to noise floor issues.
Is it safe for the C-DSP and the Porsche PCM for me to try running the PCM speaker leads into the low level inputs of the C-DSP? I’m concerned I would overdrive the C-DSP input and/or damage the PCM if I have the negative speaker leads connected to the negative RCA barrels. I have not seen any definitive documentation on if the RCA/low level ground sides on the C-DSP are isolated to be used in this way.
It’s as if the Porsche high-level isn’t quite high enough for what the C-DSP expects. Is there a way of adjusting the input buffer on the C-DSP so it will allow a little more thru? Replace some resistors on the board, perhaps?

Lots of views, but no feedback. Oh, well.
To anyone with similar noise floor issues, send an email to support. They had plenty of suggestions and got my issue resolved successfully.

DO NOT PUT HIGH LEVEL SPEAKER OUTPUTS TO THE RCA INPUTS!!!!! Resistors or not.

You will destroy your C-DSP. -10db on the input side is fine, that leave you 10db of headroom for EQ'ing. If you EQ gain on any channel exceeds a total of +10db you will need to reduce the input gain even more. You need to understand gain structure and clipping better before you set out again.

Thanks for the response. I did not write out the resolution to my issue precisely because it conflicts with the generally good advise of your ALL CAPS statement. Only after some back and forth with DevTeam/Support and a number of tests, they decided otherwise.
-10dB on the input meter with my volume knob maxed at 100% with 0dB test tones was a problem. The music I listen to has dynamic range, so 0dB test material is unrealistic. I had to crank my amp’s gains just to match the output of the OEM system. This introduced too much noise. If I was at -10dB on the input at 75% volume and more reasonable -5dB or -10dB test material, I would agree with you.
As a side note, I cannot imagine ever boosting a signal in the EQ by 10dB. There’s a different problem to be addressed if you need to do that!
To anyone else reading this with similar issues that I had, please contact support before you give up on your C-DSP. There are some things that aren’t “in the manual” that you might be able to try, but please don’t plug your speaker leads into the RCA inputs unless specifically told by DevTeam to do so.