Hi. My budget is about 90$ tops, and I'm not sure if I should buy the Ultimate Ears 600, or the UE500 with a Fiio E5 amplifier.
Which option is best for Rock music, to be played with the SanDisk Sansa, Zune or HTC Desire?
As a general rule of thumb, you should get the best IEM you can afford first before thinking about amping. In this case, UE600 looks like the better choice.
Neither, if you like the UE sound (which I do) go for an older pair of SuperFi 5 Pros or Triple-Fi10s. Both sound better than the newer (Logitech) UEs and BOTH HAVE REPLACEABLE CABLES, which is a big deal if you plan to own these beyond the warrantee period as UE cables only last about 6 months max of regular use for me.
No, it's a bit confusing because UE did make a Super-Fi 5 and 5vi that has since been renamed the UE600. I had a pair of those and they are decent sounding, but lacking in build quality and durability.
I am suggesting the Super-Fi 5Pro or the Triple-Fi 10 (aka TF10, TF10Pro, TF10vi), which are older than the Super-Fi 5 and Super-Fi 5vi, have the replaceable cables, and better sounding (especially the TF10).
And $130 is a very god price for the TF10, probably average for the SuperFi 5Pro, which are getting hard to find. Check the FSoT forum here. You are better off spending $100-$150 on these than $75-$100 on the UE-600 or Super-Fi 5.