Hey Duncan, what tips did you settle for in the end? I've been rooting through my 'tip' storage for alternatives, and I've settled for the UE single flange ones for the moment. So after all the tip fiddling, I've only had about 20 mins proper listening time so far

Anyway, initial impressions are very good, they're very clear and focused but without being cold. They're not nearly as thick as the IE8 which is good, because despite the fact I loved the IE8, I did yearn for a little less thickness sometimes. The bass is the real surprise though, it kinds of comes out of nowhere and whacks you round the head with a baseball bat. I like that! Oh, and vocals sound especially clean after the IE8.
Okay, need to do more listening now

erorax-
Before the X was released, I'd been reading up on the S9 quite a bit, and a couple of things put me off; this from ABI:
"Testing it with some lossless FLAC files against a few other players I did find that it started to fall apart at higher volumes"...
They also said the Clip handled louder volumes better - and then this from cnet, who said it sounded gorgeous, and then in the next breath said:
In an A/B listening test, using our ultra-high-end £2,000 test rig, the S9 proved to offer a gorgeous sound quality, although it's almost identical to that of the 160GB iPod classic.
I've never heard a Sony dap described as sounding like an iPod Classic and I hope I never do, because it's a sound I don't like. I tried one for a couple of days and returned it as fast as I could (although I like my Touch 2G, just not the Classic!)
So the Cowon will obviously have its own fans and the Sony will have its own fans too. Personally, I can live without compressed lossless formats because high-bitrate lossy files sound great with the Sony, and I can use WAV/PCM for albums that need to stay gapless. Sure, there are niggles, no on-the-fly playlists and stuff, but at the end of the day I use it to listen to music, and so long as the music sounds the best it can sound, that's all that matters. If all those other features were more important than the sound, I'd have given up on Sony after my A808

Right now I can't imagine any sonic improvement I'd make to the X at all.
mosso2000 - can you plug the IE8 into something else to test them?