that is totally normal. mic pres are only on channels 1-4.
$150 is a great price. these are really useful little boxes that will grow with you (although they might get moved to the side)
i have one (non VLZ) that i used as the heart of my recording studio for a while till i upgraded. i still use it for monitoring sometimes and all the times for live work (small and good). i have even toured with it, never stored it in a case and never had a problem. hell it even got snowed on.
those 4 decent but not great mic preamps are certainly worth the 38 dollars each price tag.