The woofers are different HPM 100 = 12 inch; HPM 60 = 10 inch. The cabinets are different HPM 100 = Walnut veneer and larger size; HPM 60 = vinyl. The cross overs are also different.
I run both HPM-100's and HPM-60's on two different but both completely restored (electronically) Pioneer SA-9100 amps
The 100's have more bass. The 60's are a little more musical. That said they do have a very similar sound. but the HPM-100 just has more of it.
The 100's are real wood veneer the 60's are vinyl
The 100's are 12" woofer compared to the 60's 10"ers
the 100's are 26" tall the 60's 24" tall.
Are the 100's the 200w version or the 100w version. I have the opportunity to pick up a pair and I am trying to decide if I really need the 200w version.