The diferences are.
T30 and T50 have 15mW per channel (30 total) output while T60 has 18 db output per channel (36 total) output signal.
How notticeable is that? have no clue. (or maybe a little, keep reading).
All i know is I'm sort of disapointed of my (1 day old) T50 1Gb.
It seems the signal response is too low or something related.
I wasnt specially "surprised" by its sound when I listen tested some random songs.. but!
I (sadly) polled it against my former mp3 player, a random brand, "NEXT" 128 Mb, 192kbps/max... and the bass reponse of this old player almost floored me inmediatly.
The sound of the old player was much clearer, the bass deeper, and in general, it gave you a great hearing sensation.
After the "first impression" i did several tests... and couldnt really tell... for sure.
I still think that the sound from my old player, is sharper, clearer, with deeper bass...
( In sensations (TM), the old player made me feel like wanting to "keep hearing" the song, while the T50 were good, but didnt have "amusing" on it, like the sound was much plain, a "front" of sound, all mixed.. like all mixed and overlapping coming in the same bowl....)
This tests where made with "flat" equalizer.
Tests with SRS enabled, seemed to generate sharper sound, with deeper bass.. but the sound generated the impresion of being "overloaded", excessively enhaced.
(But equalization and sound "enhacement" were not the subjects of this test)
Would like to be really mistaken, .. the t50 makes so much sense in everything else... that failing at sound quality would be a disaster.
Im using Senheizer HD 202 headphones to do the tests.
(not great, but much better than what this player is shipped with).
Please, some other T50 owners, post your impressions!
Also, t50 uses AA batteries, while T60 uses aaa (and is somewhat smaller.).
The players use different firmware versions aswell, so, there must be further harware variation.
T60 Specs
T50 Specs
T30 Specs