The Jaaag passed it's MOT last week (needed rear ARB bushes, headlamp alignment), which has persuaded me to keep it on for another year. I was sick of the rubbish audio and playing my meagre MP3 collection via a unreliable cassette adaptor though, so I've given it a massive-ish upgrade.
First step: upgrade the front speakers. Old ones were shot, and an unusual size which meant I had to lash up some adaptors to fit some 6.5" Focals. I used uPVC soffit board for this - it's cheap, unaffected by damp and easier to work with than MDF.
Snug fit for the Focal ISC165s. They had good reviews, are reasonably priced, and quite slim so even with the adaptor rings they were no deeper than the originals.
Step 2: underseat subwoofer.
This is with the seat fully forward, normally it's hidden. It required a permanent 10A feed, which I was able to take from the power-seat feed. There was also a connection to the system control lead on the head unit, the RCA connections, and the wired remote control. Routing these cables was a bit of a headache; in the end I removed the seat and ran them in the small gap beneath the seat runner. It's held in place with some industrial-grade 3M Velco strips.
Sub remote lives where the ashtray used to.
Step 3: DAB antenna, or rather this stick-on effort that came with the head unit. The only feasible spot is the windscreen, but it seems to work well enough. You can get adaptors to split a DAB feed from a standard FM antenna, but reviews suggest it's a bit hit and miss.
Step 4: new Pioneer mechless head unit, with DAB, bluetooth, USB and line-in connections. It's quite a subdued design without any MEGABASS button or similar bollocks, so it doesn't clash with the rest of the 19th century dash. It required a DIN adaptor, and a wiring harness adaptor (both from Audioleads).
Step 5: Spotify Premium. I create playlists on my PC and then download them onto my phone (limit is 3300ish songs). Get in the car, start the Spotify app, the head unit automatically connects to the phone and starts playing. Use the controls on the head unit to switch tracks, etc. Magic!
It now sounds REALLY GOOD, and the sub makes a massive difference. I left the dash tweeters which are doing an adequate job, and the rear speakers are mostly faded out. It could probably be improved further by some mid-range speakers in the A-pillars, but at the moment it's very discreet and original looking, which I like.