I'm afraid I'm not a raymarine fan, simply for it's construction in comparison to other makes. One of the centres I worked at used a raymarine as it's base station (in fact, it could well have been a 54E!) and it was dead within a season. Bought a pair last season for our ski boats, one of them still goes (ish) but the other is knackered too. Having said that, it looks like it's been superceded by the 55E - which I haven't used!
I personally would go with something along the lines of the Icom M421 - having put one of these on one of my old work's ribs. Well built (surving even commercial centre rigours!), fairly small, lots of features, can't go wrong
Obviously, yours won't be getting the same abuse as that recieved at a commercial centre. The raymarines are about the same prices as Icoms, you've just got to hunt around for deals. The Raymarine's coming in at £169 from chandlery.biz, and the Icom from Sail GB at £169.95 (both first google results
). Go into a marine electronics shop and have a look at them both before you commit though.
I'm sure someone more qualified can answer your audio questions!