ive got same issue. had all sorts of probs with head unit in the end went and bought a jvc so heads up is fine. cars already wired in for amp and sub. just taken my parcel shelf out until i can suss what to do.
ive got a set of 6x9 alpines look really nice but thats the prob dont want them looking really nice to thieves. also speaker shelf is damaged on corners mk2b punto 3 door type.
my options as i see them.
1. repair the round corners with p40 put the alpines back in and cover the whole thing with black speaker material.
2. get a new shelf £20 and re fit alpines and rely on the rear tints goin in.
3. 18mm mdf shelf im a carpenter.
4. 2x9mm mdf glued together but cutting the speakers in so resembling oem shelf.
5. as 4 but dropping a 40mm deep box all round the bottom.
im thinking of the wieght issue of the mdf shelf to be honest