Theres also a possibility of a mis-matched impedance between Modwright and Pass.That would not be a problem, at least with the LS 36.5. The LS 36.5 has transformer coupled outputs, which provide a very low output impedance and do not have the substantial output impedance rise at deep bass frequencies that is common among tube preamps having capacitively coupled outputs.
See this post by Dan Wright of Modwright.
I have no knowledge as to whether or not the same holds true for the LS 100, though.
Nevertheless, as I indicated earlier my vote is for VAC, with a suitably paired speaker that will give you the kind of bass reproduction you are looking for.
Regards,
-- Al