So finally got some upgraded sound installed.
Went with the following :
Headunit: Pioneer DEH-8750BT -
http://www.pioneer-car.eu/au/products/deh-x8750bt
Front: MTX RTS502 200W (5.25" + tweeters) -
https://www.autostyle.co.za/car-aud...systems/mtx-rts502-5-2-200w-split-system.html
Rear: MTX TRC803 8" 300w Limpids -
https://www.autostyle.co.za/mtx-trc803-8-300w-3way-limpid-speakers.html
All powered by a good 4CH Amp.
I'm no audio expert in any way but to me the system as a whole sounds very good. Decent highs and great mids. Of course lows are lacking slightly as only a Sub can provide those but it's more than adequate for my needs, may consider a removable sub box in the future.
The headunit is quite pricy but I went with it for a few reasons. It has colours that almost exactly match OEM interior lights. And is capable of showing 3 lines of info instead of the usual one. Works great while browsing folders on a USB like I usually do (See pic)
The front speakers I really wasn't sure what brand to go with, there isn't a great selection for E36 fronts (5.25") but decided to go with MTX as I've heard good things.
The rear speakers are great, the mids are excellent and no backboard cutting was needed as the old nokia speaker boxes were just modded to accomodate the larger speakers.
In general i'm very happy with the setup, it's no bass boxer but it sounds good. I would recommend a similar setup to anyone with an E36.