It would be hard to put a number on the HM-801 versus T51. The T51 is very very good, and I find it to be above even the Imod. But at the end of the day, it still sounds like a portable player, whereas the HM-801 is totally in a different league, in that it sounds more like a good desktop CDP. The difference is subtle, and whether the extra dollars is worth it will probably depends on your headphones.