1) go into the test menu of the ms-8 (hold left right left right each for about a second, or until you see the screen flicker)
2) go to Output Identification
3) Set ms-8 volume to less than -25, say -30
4) you will see a list of all your channels. Click on the centre channel and it will play pink noise through that channel only. Note SPL at driver head position in db. You can use an iphone app for this, i use an app called dB Volume as it has a slow response so its easy to measure. Make sure you set it to C weighting.
5) click on your driver side mid/tweet channel. Adjust amp gains so it matches centre. However as this is amped even on the min gains it may be a lot higher. Note this db level.
6) repeat for driver side underseats, adjust gain and note db.
7) repeat for driver side rear mid and note db
8) hopefully at this stage most of your drivers are within 3-4 db
9) now increase the [b]ms-8 volume[b] until the SPL of your drivers is roughly 55db. To measure this just go into 2-3 of your channels like earlier
10) now try recalibrating at that volume.
If you're still getting bad results try up to +3db or -3db from that calibration volume. If its still bad then bridge the amp to the woofers so the rest of your speakers level match. In my opinion this would work well.
I wouldn't really advise ditching the ms-8 and amping, assuming you started off with the base spec. You can make this work, its like a marriage. Just needs a bit of effort.
2008 E92 335D SE
2010 E90 320D SE
1994 E36 318I SE
1996 E36 316I SE