WTLC woofers are unique
To my knowledge the woofers in the WTLC's both forward and down firing pairs, were unique to that model. I speak from experience having been in a similar position as you are now when I was getting my WTLC's together. The woofers are doped paper cone drivers similar to the one's found in the monitor series except of course being 8" instead of 12". The doping, which was a tar like substance, was applied by infinity to the raw drivers to alter their resonant frequency and in the case of the WTLC, a heavier coating of the "stuff" was applied to the bottom firing pair than was applied to the front firing pair to create what Infinity referred to in their marketing material as a "mechanical crossover". Otherwise the drivers are identical. I actually ended up buying a beater pair of WTLC's just to end up with a full set of properly doped woofers.
A significant number of WTLC's that come up for sale are missing some or all of the original woofers.
Attached is a brochure for the WTLC that describes the woofer configuration.
