if it was me i'd stick with the 555 but drop in a lo pro,
sell the crate, and put together a rack head, with some 4x12 cab
bear in mind i'm talking about used gear and in US$
a nice tube preamp can be had for a huge range of prices
but i got a Mesa Quad for $320 and have seen an Engl e530 for $350
so let's say preamp=$350
i picked up a peavey 50/50 (poweramp)for $250, a bargain i think but obviously possible
as for a cab, i'm not really sure how much these are going for...
i'll take a guess at $300?
plus an actual rack case for $50
so there's a setup that beats the TSL100+cab for $950US
and you can always chop and change or add rack components
by the way, i don't know what things are like over there but here there's no way i could trade a 555+gx212 for a tsl100
so you're probably gonna have to add cash+$ for the cab+$ for the RG1550, it's probably gonna work out more expensive than the extra $950 for the rack setup
hope it helps