Can I use any subwoofer to do the subwoofer crawl? In other words, can I borrow a friend's REL subwoofer to find the best position for, say, an EP500?

Can I use one subwoofer in the listening position to find the best two positions for a pair of subwoofers?

Axiom M80s + QS8s + VP180 <-- Pioneer VSX-1120-K <-- Squeezebox Touch / XBox360 / Oppo BDP-93