I'd go with the LS-100. The highly resolved, ever so slightly warm (for a solid state amp that is) and inner detail and micro-dynamic finesse of the Pass amplifier would be complemented well by the richer texture of the LS-100. Personally, I think a 6H30 preamp here would be a bit boring.
I know a lot of people aim for absolute neutrality, but you know, one person's neutral is someone else's cold fish. Fortunately, I think a Harbeth owner would appreciate that sentiment.
When I had the LS-100, it was outfitted with Sophia Electric 6SN7 tubes and Mullard 5AR4 rectifier.
I presently own the Atma-sphere MP-3, which I think is slightly more neutral but just as beautiful.
Best 6SN7 preamplifier I've heard is the TRL Dude. I owned one briefly, but its chassis was too large to be suitable in my shared listening room. That might not be a problem for you.
As for DACs, I think one of the best values out there right now is the NAD M51. I'm really impressed with it, and having been through many DACs over the years, I can say this one is a real standout. At least it is in the $1500 - $3000 range.