Hi there, the bass has an ACG EQ01 filter pre-amp from http://www.acguitars.co.uk/
This features two low-pass filters, one per pickup and a global high-pass filter, giving you the ability to EQ each pickup independently. Its similar in concept to the filter based pickup system from Wal. The internal controls (which I admit I have never touched) include gain adjustment for each pickup, treble path selection, and a trim pot that allows you to choose which pickup supplies the feed for the high pass filter.
The small switch on the face of the bass allows you to select the piezo pickup in the bridge or the two magnetic pickups and the small light indicates that the battery status is good when you first plug in.