e36 Radio - no power to head unit

Replacing e36 vert aftermarket radio with CD43 - wiring help/analysis
I attempted to install a cd43 radio I got from ebay in today, and ran into some wiring problems based on an install from the prior owner.

I connected the CD43 to the factory wiring harness, and couldn't get power; I noticed that there is a yellow wire coming separately out of the dash and running into the aftermarket headunit wiring harness, NOT via the stock wiring harness; the wire harness notes this is the 12V power cable. I'm not getting any power to the new CD43. When I plug the old rig back in, I don't get power there anymore either. I checked fuses under the hood and the back of the headunits, everything looks OK... In typical fashion, before it can be upgraded, I must break it!

First things first, when the prior owner put in a new, Sony Xplod head unit, the shop he used bypassed the amp entirely. They tied into the existing wires with snap on splices, which I hate, but a few other things happened that are worth note. What are the implications of this on a new "stock" radio?

I also ran into a few other problems...

1) The sliding cover on the factory wiring harness snapped off, so now it only "plugs" into the back of the CD43 or aftermarket wiring harness, there is no plastic vertical sheeth that locks the harness into place. In of itself, would this cause the whole rig not to get power, or only leave me vulnerable to it coming loose (it plugs in VERY tight, hence why it broke).

2) What do you make of the yellow power wire coming into the aftermarket headunit? Is it possible to power the CD43 without the factory amplifier? See pictures attached for more details...

I plan on replacing whole system with an aftermarket amp, but with the CD43 radio using line output converters or high level inputs on the new Amp. Will any use of the CD43 be possible without an amplifier?

Thanks everyone, I would greatly appreciate your help before I tear the thing apart further (or cough up several hundred dollars for a professional repair)...

Have you had any luck yet?