it would be very strange for a triple BA not to "suffer" from added impedance. I couldn't find an impedance graph response for the w3 but with the triple fi we have plenty.
from ****ty approximates because I'm not going to spend the day on this, the impedance graph on tf10 goes from around 54ohm @1khz to maybe 7ohm @10khz.
with let's say 3ohm source going with and without the 50ohm adapter would make a variation close to 10db between 1 and 10khz.
so you should clearly be able to hear it (the 10khz go down big time with the adapter so look for the cymbals with and without adapter).
now if the W3 are close to W4 or UM3X in impedance graphs then it might even be a good thing to add the adapter, but in any case there will be a change in signature.
it is true that making the impedance go up could be a solution against hissing. it doesn't remove it but lowers it compared to the music (in fact everything goes quieter, but pushing the volume control up only make the music come back up and let the noise where it is).
so I'm not saying not to try it (it's not super expensive anyway to get an adapter on eBay), just to warn you it will change the signature in some ways. surely less than the super impedance picky tf10.
about the sansas, they don't really hiss and that is great, but they make an electronic noise every 30s or something (never cared to time it) and it lasts like 2secs "dzzzzzzzzzzzzzZit" yeah I'm a pro noise impersonator. so with sensitive IEMs it might drive you mad even more than the hiss of your phone as it's not permanent.
to fix hissing for good you have 2paths:
-find a non hissing dap. my cowon I10 is a pretty cheap **** that really doesn't hiss at all. but you have to survive the ludicrous UI. X3 doesn't hiss but you have to like the sound signature so I would recommend listening to it before buying one. to me it's a lot better than the cowon in a lot of aspects, but I also believe the average joe would have a better time with a cowon and all the sound tweaks available.
-or get a non hissing amp (most of them), but you will end up paying more for something bulkier.
I'm really really picky on hissing stuff and didn't find the perfect solution yet. my lightweight solution is a clip+ and some ethymotics for max isolation, or clip+ and IE80+impedance adapter(they don't change sound signature from impedance variation) when I'm missing my bass too much and don't need isolation.
and with quality IEMs I add an amp
.
