[rpg]

Thanks for the input. OK, there's clearly strong opposition for my coaxial underseat idea! Would you go as far to say that even the stock base underseat subs would be better than doing that? Then like ctuna mentioned above I could look for some HiFi underseats, eBay might be my best bet.

The Axton A590DSP you mentioned is very nice of course but best price I can find is €270. I've managed to pick up the Pioneer GM-D1004 for £60. Yes gain is fixed according to spec but I have speaker level adjustments via the HU, any use? I will be connecting the amp via the 4 low level RCA plugs on the HU. The amp appears to be 2ohm stable also, so if I get the HiFi underseats they'll be ok (I believe they are 2ohm vs the base audio which are 4ohm).