I have a 4PRO that was converted by Mike at Panic (very handy as I live very near him). I agree that he does not recommend using a step down transformer for a number of reasons - if you want the reasons then give him a bell, but I trust his advice.
The transformer you have in the 6PRO *should* be multitap, which means you don't need a new transformer, but if it's anything like my 4PRO, then there is some changes needed to the internal circuit breaker also. Gonna cost you about £120 or so, but better and safer than carrying around a great weight of a transformer.
Bear in mind they are extremely busy so don't expect a quick turn around unless you can deliver and collect yourself. Ask Toasted..;-)