Exactly - an "off the shelf" converter will not be able to supply the power conversion needed for when you get power spikes - IE, a track that suddenly demands a shed load of bass for a second or two.....

When me an my bro set up his Soundstream Ref 700 amps in the living room, powering a pair of Dynaudio components and a JL sub, we ran em off two boat batteries Big big big bastids. Hooked em up to a linked charger and had no probs