Well hell yeah! i'd be happy to help.
I just fitted new front and rear. Easy peasy.
The speakers you need are 17cm speakers. Jut use a screwdrive to wedge off the grilles. This was easy because if you look carefully you can see the metal clips and clip off there. No need to remove door panel.
Then its a simple 4 screw arrangement. The speakers i got just slotted straight in with no adjustment on the brakcets. Then the grilles went straight back on without issue.
, i did have an issue with the wired connectors. the connectors on the speakers were a large and small (positive and negative connector) yet the wire from the door for the speakers were in a yellow clip side by side and were not different sizes. So i had to rip off the yellow connector and seperate the wires, but i had no idea which was positive and which negative. So ended up looking back on the ISO clip that goes into head unit and worked it out with a bit of advice from here, but also if you connect the wire before you screw the speaker back in you can tell if the connection is wrong because it will sound like the sub part of the speaker has blown. get it right and its a nice clean sound. (still not sure if its 100% right but sounds ok)
Also i order a set of pioneer speakers that included new tweeters which i was told were ok for a 156 but when i got to the tweeters the fixing arrangement was not standard for my new speakers to the bracket of the door card. as such i cant use the new tweeters
but the i dont think its an issue as the standard ones are actually ok
Also the connector for the standard tweeter wires is weird and so i would just leave it.
The Head unit was dead easy. Pull out standard one. connect new one with ISO Din connector (supplied with unit) and slot right in, not forgetting the Alfa facia plate.
This is what i ordered from https://caraudiosecurity.com/catalog/index.php
1 x FP-09-01 - Alfa Romeo 156 02/98> facia £10.00
1 x Pioneer DEH-P77MP - CD/MP3 PLAYER £210.00
1 x Alpine SPE-1702 - 17cm speakers £39.99
1 x Pioneer TS-1785 - 17cm custom fit speakers £44.99
I would leave the Pioneer next time and just get 2 x alpine for front and rear.
good stuff cheaper than anywhere else, but took a while to come as speakers on back order. The car sounds really good now.
No bloody AM reception tho but i believe this is standard on the 156.....
Hope this helps. any further queries let me know!