2014 CX-5 Replacement Head Unit

2014 Mazda CX-5 GT
First time posting here but I've been reading a lot of the threads. I've never been fully happy with the infotainment system from the factory, and finally (years later) have decided to take the plunge and replace my head unit. For now, I've just put in orders for almost everything that I think I need, based on my research on this site. Vehicle in question is a 2014 CX-5 Grand Touring with Bose.

What I've ordered so far:
JVC KW-M740BT ($259.75 on sale at Frys)
AX-MAZCAM ($7.46) with SMAKN 12V/6V transformer ($6.90)
Metra AX-USB-35EXT ($10.30) I'm hoping this is long enough to run through the center console...
MAZK855X ($74.12 on sale at Amazon) which appears to include:
  • RP4-MZ11 for controls
  • MAXK855 Replacement Frame
  • Metra 40-HD10 Antenna Adapter (or similar)
For a not bad total of just under $360.

The reasoning behind the equipment selection:
  • RP4-MZ11 was required over an Axxess ASWC-1 or PAC SWI-RC because of Bose system and to make the head unit pick up on reverse signal for backup camera. Turned out okay because I was able to get the pack on sale, so pricing was a wash.
  • AX-MAZCAM is a prebuilt harness which is nice, but the OEM Mazda camera requires 6V so I will have to splice the transformer in line. Could have also gotten the AX-MAZCAM-6V but for some reason those have really bad reviews, so I wondered if the transformer was putting out 'dirty' power i.e. not consistant 6V (it looks cheap...)

Some other questions before I get started, in case anyone has some tribal knowledge to share.
  • On jlcpremier's thread I found, the interconnect spreadsheet shows that the head unit's parking brake wire would connect straight to ground, which is odd because it also shows that the RP4 has a red/white wire for parking brake output. Is there any advantage to directly tying the head unit parking brake wire to ground (ie, avoiding any 'safety' functions?)
  • Edit: I just realized this question isn't really applicable - the JVC preamp outs are for high/mid/low, not front/rear/sub, so I'll go with hooking up the RP4 wire connections instead of the head unit connections. I'm a little confused about the Bose amp connections. On the thread mentioned in my first question, jlcpremier used an RCA splice (Kicker KISL Speaker wire to RCA adapters) to connect from the RP4 harness to the bose amp. My JVC manual says that the RCA connections on the back of the head unit (front/rear/sub) are pre-outs for connecting to an amp... What should I be connecting in this case?
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