Reddit mentions of Clarion EQS755 7-Band Car Audio Graphic Equalizer with Front 3.5mm Auxiliary Input, Rear RCA Auxiliary Input and High Level Speaker Inputs

Clarion EQS746 1/2 DIN Graphic Equalizer with Built-in Crossover https://www.amazon.com/dp/B000EZV3T8/ref=cm_sw_r_cp_apa_t5Nxzb47ANXQB

I'm not totally sure I understand your question, but let's see if this helps clarify things.

The easiest way to send the audio signal from a Nexus 7 to that amp would be a mini jack to RCA cable back to the amp, then RCA splitters at the amp, and adjust your fade using the amp levels.

It looks like you might want control over fade/bal in the dashboard, in which case the device you linked to looks similar to this one, which I've had good results with in the past. One RCA in becomes 3 out with separate level adjustment and overall EQ.

That's the direction we're going. You'll be missing:

• AM / FM / HD / Sat radio (no big loss, replaced by Pandora and streaming internet radio)
  
• CD / tape player (who cares)
  
• Balance (I keep it centered anyways)
  
• Fade (I push towards the front, this can be accomplished by adjusting amplifier gains for front/rear)
  
• Volume - I like having a volume knob
  
• EQ - You'll lose out on the ability to fine-tune the output for your car.
  
• Separate subwoofer volume - I adjust this now and then. Can sometimes be replaced by a remote knob to the sub amp.
  
• Display - My phone auto-locks, display dims after inactivity, and it's hard to read in direct sunlight.
  
  So most of what you're missing out on is sound processing. Get an equalizer and a good dash mount for your phone and you're golden. I think you're on the right track and this is the future of car audio.

Receiver

DAC

Both for $100.