Bill - Fair questions. One Harbeth dealer I know does not favor the HL5's because he considers them a bit bass-heavy. I've heard something like that elsewhere, which suggests to me that the "leanness" you report in the M30s probably reflects a consistent difference in the speakers. I also recall that one of the on-line reviewers described the M30's in such a way that I can imagine them seeming perhaps more forward than the HL5's. However, I have never heard the HL5's. In fact, I hadn't heard ANY Harbeths before I got my M30's. I had been using Vandersteens for some years before that and was suffering from substantial "detail fatigue," and one evening, after suddenly getting frustrated with the Vandersteens one too many times, located a pair of M30's and acquired them in the space of about an hour. It was one of the best things I ever did.
My room is not large (14x19). In my room, I would characterize the M30's as somewhat fat sounding, in a very pleasant way. They are 3 feet from the rear wall, and set up a pretty darn good soundstage (although they take some work, positioning-wise, and do have a sweet spot). They have very nice bass for a box that small, and the top is smooth and easy, with detail, but not drowning in it. However, I will say that they are very sensitive to whatever you run them with...with the wrong pre-amp, amp, etc., they can sound bright and irritating and probably a bit forward. As mentioned, I found that tube gear produces the warmest and friendliest effect. How "forward" they sound depends at least somewhat on what you run them with.
In your space, you may like the C7's better. As you no doubt know, the C7's were recently revised to present more detail. You may or may not prefer the newer version...I haven't heard them, but shortly after I got the M30's, I heard some of the older C7's at a dealer, and was favorably impressed. They are smaller than the HL5's and don't have the super tweeter of the HL5's.
Feel free to email me direct if you'd like to discuss this further.
Best regards
