Well I have a custom system in my 01 ssei, I didn't hook up a 6disc changer so I can't help you on that. My installer did pull out the Bose/Monsoon radio out. I was there it is a ribbon that plugs in. My Alpine now fits nicely with no problems.
Now couple things though, I did lose all my door chimes and can no longer talk back/hear the wonderful people at Onstar. Didn't plan on re-subscribing the previous owners plan, it'* like $350 a year. I've got a cell phone. I can't really think of anything else that a lost. Could of kept the Onstar hooked up but would of had to buy some harness for $250 and hook up an extra speaker and mic, not worth it to me.
My installer did say that when everything was done on my car, he said he had some crazy feedback/distoration/alternator whine like your talking about when he started. He told me he had to go through all the wiring/grounds to fix the problem.
I also got the Alpine/gm steering wheel module, keeps the steering wheel controls for like $85 I think. Also reminds me that I DID lose the radio station # on the H.U.D. Oh well, Hi-Fidelity sound is well worth the price.
Stereos are my passion.
Check out my stereo here http://www.cardomain.com/id/taylordssei
Sorry I couldn't be more help, Good luck.
Your installer can call mine if he needs help, 1-630-435-0690 Tweeter in Downers Grove, IL ask for Tiger!
2001 SSEi 13.731 @ 101.59--->PICS HERE <---
--Intense PCM--2nd gen LSD--3rd gen Rockers 1.9 --#105lb springs--oil restriced pusrods--Intense shift kit--TEP CAI--ZZP mod 3.4/3.2 --IAT relocate--TOG silver ceramics--SLP CAT--o2 fake--160 stat--PRJ 10.4mm wires--Autolite 104'* @ .055--MAP TB heat shield
--Custom mesh grill--Cleared front and rear corners--Angle Eye'*--Silverstars 9006+9005+H3--PONTIAC 3rd break light overlay--Embrodered PONTIAC head rest wrap--Arrowhead inlays for front+rims+steering wheel--Zaino polish
--Alpine IVA-D300 7in TV--two 10W7s--JL amps 1000.1 & 450.4--MB Q'* 6.5in Comps--Optima yellow top--5 farad cap--lots of dynamat extreme--Custom install w/ plexi and mirrors--Sirius radio--compete in Sound Quality!!!
------PROTECTED BY VIPER!!!!!!!!!!------