Hi 2x6spds,
A couple of points: It seems your Velodyne sub has a "Direct" setting that bypasses its internal crossover. Use that setting if you are using the Onkyo's built-in low-pass crossover for the line-level sub output. Set the Onkyo's sub filter to 80 Hz.
If you are using DVD-Audio, I'm surprised that the Toshiba player has bass management for DVD Audio. Most do not, but maybe your's has. You'd be going through the 5.1-channel analog inputs for DVD Audio, correct? (You can't go digitally because DVD Audio is decoded in the Toshiba player, not in the Onkyo).
If possible, designate the centre, surround and back speakers to "Small". That sends all bass below 100 Hz to your sub. You can designate the Main speakers as Large, but as Ravi points out, you may get too much bass because then the sub and the mains will be duplicating bass output below 100 Hz.
You can switch in the Velodyne's crossover if you want, but only if you can't get a satifactory subwoofer/main balance using the Onkyo's 80-Hz crossover setting. Set the Velodyne's control it at its highest frequency (150 Hz?), then gradually reduce the frequency until you get a good sub/main system balance.
Get a setup disc to help you with this. The new Sound& Vision Home Theater Setup DVD is easy to use and has lots of test signals for corrct subwoofer/receiver/main speaker bass setup. It also has excellent test patterns and instructions to calibrate your TV monitor.
Regards,
