Hi Splatrat
I recently installed sub and amp onto the standard H/U
I used Davros
guide to do my install and his instructions were great, link
http://www.seatcupra.net/forums/showthread.php?t=117628
The only thing i found different was that wire required to tap into for the REM signal to the amp. Instead of the "uB CDC" being tapped into it is actually the "CDC" number 10 (see Blaupunkt diagram in link above or the top of the H/U). I used an old wiring loom from a sony system, cut out one of the small pins from the connector and fitted it into the Seat pin connector (in the correct position so that when it is plugged back in my pin and wire were plugged into the "CDC" slot). If you do this with the H/U out the dash and check with a multimeter u should see when ignition is turned on that you have yourself a +12V signal and when ignition off (and key out) the signal dies.
Goodluck bud