Without any playback in Cubase4, I have 50% ASIO being used. Is there a way to reduce this in order to provide more head room?

The reason I ask is because when I do go to playback with effects, I am hitting 100%. I have read that I should try increasing the buffer size, but when I do this buffer size is not an option. I am doing playback of 22 tracks through a Firepod. The only option I have going through the control panel is latency and sample rate.

2.8GHz Pentium4
1.5Gb RAM
XP Home
Firepod