mixmstr

Hi ,
Forgive me, but this is a little new to me. I have a XLS 1500 amp that I am using to power 1 Peavey PV118 Sub(400w Program Power 8ohms). I currently have the amp setup in Crossover Mode(Input Y XOVER) with the sub connected to channel 1 Bannana Plug. If this is correct, what freq. crossover point should it be set at? Does this setup provide 300w to the sub other than the bridge mode of 1050W(which I take that I should not use). I just want to make sure I am getting the most out of the sub and I'm not overdriving it. Also, I have another amp that is running my mids/highs speakers. This is being using for a dj setup coming out of a Rane TTM57 mixer. Appreciate any suggestions.
Thank You,
Alex