Was asked about my perception of the UM56s on the UM3X, since I had talked about getting them for a long time and finally have them. Well, they are the best tips I have used with the UM3X. They give the Westones another dimension, a little more detail, the bass seems more solid/extended. I am glad I got them, and at $115 including impressions, I got a very nice deal.
There is one weird issue, and I have talked to Westone about it. The UM56s, now and again, on either side, seem to slip off the sound tube and the driver housing just falls out. They are snug when I insert them, but all of a sudden, they just pop out. I have black otoblast material, which is the soft silicone. I contacted Westone, and they said it could be the hole was not bored properly. Might be. It doesn't always happen, but it does. And, now I can use the UM56 with the Image S4s as well (also an excellent match), the same thing happened today.
It doesn't seem to have anything to do with the impressions, of course, but the Westone rep said I should contact her and maybe see if they can do them again. Not sure how that will change anything, really. I may ask her to do them again and try them in vinyl, the harder material, and see if that makes any difference. I can just pay the difference if they cost more, I guess. I have to call Monday.
Finally, if you leave them on the UM3X, great. But when I take them off, say to use the Flex mediums, figuring out the angle is sort of a pain. I've decided to use the UM56 for sitting and listening (planes, trains, etc.) but the Flex sleeves for dog walking, my twice daily listening sessions. Just easier to remove them and the iso is a little less of an issue (hearing traffic, etc.).
But on balance, I am glad I got them.