There are four bolts holding the electronics rack to the floor of the car Richard, from memory 10mm socket and extension required to get at the back ones. The whole cradle will then slide away sufficiently to get at the connectors or, indeed, to remove the amp.
From your further description I am of the opinion that the connectors need to be checked for security and if they are satisfactory, I would try another amp.
It's unfortunate that you are some distance from Wolverhampton otherwise you could have turned up at my house and I would be able to fit another amp for confirmation of the fault and my friend Denis could probably locate a permanent replacement if it was required.
If you're passing this way (less than 10 minutes from M6 J10a) at all I'd be happy to take a look for you. Alternatively, maybe somebody you know locally might be prepared to let you swap out the amp.
Those are my thoiughts as things stand. Let me know if I can help.