Good to know ;\)

Looks like they replaced the built-in speaker-level high pass filter with an optional line-level filter box that goes between pre-out and amp-in :

http://www.hsuresearch.com/products/high-pass-filter.html

Seems like a nice idea - switchable frequencies and 12 db/octave instead of the 6db/octave in most of the passive filters.

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8