Sblagg you can build or buy a line level passive crossover which you would place between the pre and the power amp. I believe you'll want a second order for that ADS. There are a few sites that will give you the formula to build them. Which in turn allows you to use better quality components. Car audio guys use Fmod's which will work also if you aren't a DIY type.
Either way should work well for you.
Either way should work well for you.