I'm no engineer, and make no claims to being an expert, but consider guitars and how and what they're constructed from- the type of wood, how the neck is attached, the type of strings you use- to name a few variables.

Some guitars sound inherently brighter, some not, and guitarists take that into consideration when they're looking for their sound. I have a Strat with a maple neck that sounds far brighter than my Strats with a rosewood neck. The bodies of each are also made from different woods. I believe these variables ultimately have an effect on the overall tone.

So, no, I don't think you're hearing things. The new machine heads, being of better quality may be allowing the strings to resonate better- hence, the "boost" in sound you're hearing. Just like the block you used- possibly the heavier block resonates with the body that much more, therefore the "boost".

But say, you had a guitar made totally of cement; will you get that boost? I really doubt it, as I don't think cement would be a good conductor of of the string vibrations. Maybe for speakers that icicle gave in his example, but I doubt it when it comes to guitars; I think of guitars and all that they're made of working in concert together as opposed to one piece working against something. Only exception I can think of, are semi-hollow, or hollow bodies, where a player might stuff the guitar to reduce feedback. In this case, I think they're trying to reduce resonance.