411 audio systems

[AndrewA]

For what it's worth I went through a similar mental process. I've got a 410 which from the factory has an overhead speaker between the driver and passenger and one speaker on RHS of parcel shelf. I considered putting speakers in the front door cards, in the kick panel under the rear seat squab and the parcel shelf. I also looked at the retro head units. In the end I went with getting the best sound I could from new speakers in the original locations and the most discreet modern head unit so I had all the connectivity for the rare occasions I might use it. My reasoning was I didn't really want to start cutting additional holes and if I'm honest with myself, most of the time I prefer listening to the car. If not that then Radio 4 and it's only on long motorway treks (remember them!) on my own that I'll use it to listen to music that the rest of the family can't stand!
I got the head unit sorted first (I went for a very plain modern Sony unit in the end) then spent quite a while trying different speakers in different price ranges until I got the sound that I was happy with. The dual voice option sounds a good place to start IMHO. In terms of the sound quality, it's now miles better than original but it's no concert hall. I also wondered about suppressors as the old radio would rev in time with the engine (!) but modern unit needed no suppressing and is crystal clear.
Good luck!
Andrew