AAISP staff here!
The FireBrick has a web interface as well as the ability to edit the raw xml config - it's not too bad! Also, we can configure it before shipping id you like - that will get you online and started. Quite a few customers bond VDSL, as well as some staff! SIP is normally fine - the FireBrick at your side will automatically prioritise the voice traffic. You may get some further information from customers on our IRC channel: https://support.aa.net.uk/IRC
Happy to help further.