I have an "Active 7 Smart", I believe, and a pair of the "ear defender pit headsets". It wasn't cheap - £300+ IIRC.
It may not be a current product any more but they come up on ebay pretty regularly. They are designed for bikers, so yes, helmets no problem at all. You get speakers and a mic that velcro into the helmet, IIRC. In fact, mine would have been a lot cheaper if I'd gone that route. The ear defenders were not cheap, and they are simply Peltor ear defenders with the speaker inserts and a mic boom added. Could have knocked a pair up pretty cheap if I'd put my mind to it.

The control unit has the following connections:
2 headsets
Mobile phone for hands-free (connect to phone or a bluetooth hands-free kit)
PMR / CB etc. Transceiver (provides audio in/out plus signal to key the transmitter when the VOX is activated).
Music input (iPod, radio, etc)
It gives you volume and VOX sensitivity control. When sound into the mic exceeds the VOX threshold, the background music is faded down and you can hear each other and communicate via phone / radio. After a couple of seconds of no activity, the music fades back up and the mics are muted. Sound quality is excellent and it works like a charm, although in a windy environment like a Seven you need to adjust the vox to suit your cruising speed. Shouldn't be so bad in a car without as much wind noise.
I wouldn't be without it on a long journey any more. Really superb bit of kit.

Only trouble I've had is one of the mics got a bit crackly after a rather wet tour. Just prised it apart and replaced the condenser mic element for one from an old mobile phone and bob's your uncle.