I also have 2 head units in my Miata, but i have the Empeg feeding into the AUX input on the Clarion and then the Clarion feeding the amps. The only downside to this is that i cannot use the equalizer on the Empeg when the Clarion is th source...but i can live with that

having said all that...and i am sure i have bored our members to tears with...i have chronic igintion noise on my system which i have managed to reduce it to happen when i have some hi-drain accessories on (headlights-A/C-read defogger)....

so what i did was to buy a high powered amp so that i could keep the gains fairly low and thus lower my noise floor...

HOWEVER...the amp, at 200 wpc, was a bit too powerful for my speakers (Infinity reference components) and melted the mid-drivers...soooo...i replaced them with a pair of kicker components...and i melted those too (true story...honest!)

soooo i am now upgrading to a set of speakers with a higher power handling capacity with the goal of FINALLY having my dream system...being one that is quiet and pleasurable to listen to

i dont know what car u have but this car of mine is PLAGUED!!!!!

good luck!

Ed