Then again, for the NP-30 there is the possiblilty of using it as a midi keyboard controller with, in my case the Tyros 2.

Here are some pics and posts on this subject. One setup even shows a bass pedalboard being used.

I definitely want to try the NP-30 again using my speakers. It's just that the sound coming out of it's built in speakers just sounded, I don't know, I just couldn't connect with what I was playing and what I was hearing is the only way I can think to explain it.
http://www.yamahapkowner.com/forum/index.php?topic=8123.0