And on the flip side from Russ, I've never heard the CMT-340 but have heard the entire HTM line as well as the HT-8s.
Sensitivity, dome tweeter vs. CD/SEOS WG, custom 8" woofer vs 6.5" MTM alignment, all things to consider. If you can find any fellow AVSers near you that have both (or one or the other) you should try to give both a listen.
I am biased as I own the HTM-10s, but I can't imagine you would not be extremely happy with the HT-8s. If you are in the SE MI area I would be happy to have you over for a listen (I also have an HTM-8 as center, that at a recent GTG was compared directly with the HT-8
ETA: I wouldn't describe the HT/HTM lines as neutral. They were designed to be HT speakers, so they would be better described as more forward/dynamic. There is an HF pad you can engage to take a bit off the high side if you like, I didn't find it necessary.
Also, subs like your Marty cube are a completely different beast. Can't really compare DIY/AIY speakers based on your sub experience. There's very little engineering involved in sub builds vs. 2- or 3-way speakers.