Which head unit should I fit, opinions on Kardon set up and aerial repair

[Bob Walker]

Dear All
Lockdown is giving a bit more free time to 'play' with my 'ZT and preventing me from going stir crazy! My question is, there are lots of replacement head units available. I would be nice to fit a head unit with built in DAB and Sat Nav. But which one is the best value for money and how difficult are the to DIY fit??
Also
How much improvement would I get from fitting a Harman Kardon set up??
My present basic set up give me poor reception, the disc stack in the boot has stopped working and cannot get the discs out (!).
Plus
I also suspect there is a break in the rear window aerial wiring (which repair kit is the best?)and it also sounds like a suppressor has gone!

Any advice on these matters will also be appreciated.
Bob