I have a pair of K551's, and considering that the earpads are identical, I think it's okay to post my question here.
The K551's were really cheap in a local store, so I didn't wander for very long, and bought them. Before the purchase I've read that the bass may not be satisfactory for a lot of people, but I still thought it would be good for me, because some people mentioned that the K55x series is similair to K271 MKII, which I have at work, and with which I'm happy with. Turns out, the K551 are a lot less "boomier". So I'm boosting bass using an EQ.
You've mentioned that HM5's pads offer a better seal, which may be a "deal-maker" for me, because from what I've found:
1.) The lacking bass is mostly due to the bad seal.
2.) The seal is often lost while moving around
These earpads might fix these problems, however shipping alone will cost me
$21, so I'm a bit wary about the purchase. Is the seal "that much better"? Because I am willing to spend this money if it is.
I know it's hard to "quantify"
these things,
but if you have any thoughts about my situation, please share them.
EDIT:
Turns out the earpads aren't identical at all, but, still, people managed to get HM5's pads onto the K551's