Best upgrade route from a Wharfdale PM600

[Purple Frog]

I have a Wharfdale PM600 PA, and it's struggling a bit with some of the bigger gigs I play. (I'm a mobile DJ.)

Want to replace the PA with something beefier, but a bit baffled by what I should be looking for in terms of wattages etc. One option is just to get a pair of bass bins to go with my existing setup. (Cheapest option at around £250-300.) Alternatively I was thinking of the Peavey Triflex or a pair of Mackie Thump 15s. (I like the idea of going active as I no longer have to cart an amp around.)

Any thoughts on any of these options would be most welcome!

Ben

[mr.doom]

The thumps may be a good option "if" that is all you can spend and want "new" gear although I think a decent used powered sub would be a better long term investment.

[Purple Frog]

I can probably stretch to £600-700 - does this change things? (Have also noticed a few posts saying the thumps are overrated - is there a better bet?

Also, am I better going for cheaper speakers and a sub, or spending more on better speakers?