I have the later HPM-60's , it took me a while to warm up to them, figure them out with my Yamaha gear, but I now really like them and decided against selling them...
On a whim, I snapped up a gorgeous pair of gen2 HPM-40's and was blown away by what this little speaker can do.
I liked them so much that I then bought a pair of early HPM-40's and they sound even better !
Tone is subjective, but to my ears the early 40's dig noticeably deeper bass wise , I'm guessing this is due to a deeper cone and the foam surround ?
They are also a bit smoother on the top end than the later ones. It can be hard to tame the gen2 40/60's without dumping the L pads way down. This is not an issue with the gen1.
I run both pairs of 40's in tandem and they compliment each other very well. The early version are on the bottom, and of course there is some fiddling around with the L pads to get them just right, but I
am so glad I jumped on them, My Yamaha MX-600U powers them well.
The gen2's seem cleaner & clearer, I don't think reveal is the right word, but I hear more background tracks with them, the bass is HPM, but the gen1's just have more of it.
Now I'll be quick to add that the bass though deeper, is not as clean or crisp.
The gen1's are indeed a totally different animal and I love both together.
When I want to shake the house, I run 2 pair of HPM-100 [100 & 200 versions] with a Yamaha MX1000U , and when I'm simply working around the house or relaxing the quad of 40s' gets the nod.
If the early 60's are anything like the early 40's, a quad of gen1 / gen2 together will be glorious... I have a spare set of gen1 re foamed 10's ready and waiting !!
HPM--150's are on my short list..