Well, IMO, the most important part of the system is the speakers, so if you can do it try to find the greatest 'dynamic range' you can.
The idea is that the wider the range the better. On the base side the lower the number the better (more low frequency bass) and on the other end the higher the frequency the better...so a system that goes from 10hz-10,000 hz isn't as good as one that is 5hz-20,000hz. A really crude basic rule of thumb but one that has served me well, you may need to dig a little for the info, but it is really worth it.
Also, see if the store has any old stock from last year to unload
And check any system by googling the system name+review and see how peeps like it.
________
Live Sex Webshows