With the SlimX set to about 20/40 volume, and my homebuilt cmoy w/ crossfeed amplifier connected through the line-out, set to about 80% of max volume, and a pair of HD590s, I can't hear any hiss at all. The hiss must be quieter than the background noise of my house (heating and computer fans and the like).
What i've noticed is that the hiss is constant in level, regardless of the volume setting on the slimX. So choosing your gain stages is pretty important. If I set the cmoy amp to max volume, and then bring the slimX to about 15/40, the music sounds the same level, but now the hiss is truly noticable! But all I have to do is change the gain staging a bit, and bring up the SlimX and turn the cmoy down a bit, and the hiss fades out, and disappears behind the noise floor of my house. If you were using a closed phone (or an Ety) the high level of isolation would mean you would probably still notice a bit of hiss, but even in that case, I think the SlimX's hiss can be minimized about as much as any portable player.
So while people talk a lot about the 'hiss' of the SlimX, I think its probably because they have all the gain in their amp, and not letting the slimX gain up over its noise floor. So if you are having hiss problems, try adjusting your various volume levels, and see if that fixes the problem.
All in all, i'm quite pleased with my SlimX. I didn't buy it expecting perfect audiophile sound quality, but I've been very pleased with its sound performance. It would be nice if companies placed higher quality amps in their portable players, but impetus to make batteries last longer, and make players smaller hampers any attempt to make a better internal amp. And Joe Consumer doesn't even give a poo. The SlimX has a very good headphone amp for a portable player (especially a portable MP3 player), and a good enough line-out to make a decent external headphone amp worth the time.
Peace,
phidauex
