I was at Radio Shack tonight and bought a stereo headphone adapter 3.5mm female to 2.5mm male.
It works. It is playing in full stereo.
The package has the following code on the bottom of the frong: 274-373
On the back of the package it has the same code but slightly longer: 274-0373
Go to RadioShack.com and do a search "274-373" and it pops up. Here is the link:
CLICK HERE
Please note the website is confusing as it uses the terms 1/8" and 3/32" but 1/8" is 3.5mm and 3/32" is 2.5mm
If you do a search for "274-0373" the exact same product comes up (even the link / URL is the same).
Like I said it works and is in true stereo. I've tested with several songs being played back on PowerAmp
I use PowerAmp because it can play back a variety of lossless audio formats such as FLAC (which is what the bulk of my music collection is in). The 'stock' music player can't do that heh
P.S.
I just realized that the item I got looks very slightly different than the one on the Radio Shack website yet the description and product number do match. The one that I got is a bit longer and a bit wider and is mostly smooth (without ridges) although there are some 'rings' around it (near the base and the end where the jack sticks out).
One last thing ... I tested it with regular 'normal' stereo headphones with a 3.5mm jack. In other words they didn't have a mic built in or any in-line volume control etc.
*** EDIT ***
Yes yet another edit to this post LOL
I was looking at the RADIO SHACK website again and I found an item there that looks EXACTLY like the item I bought but the model number is different. The model number on the website is: 274-0397 / 274-397
Do a search on either number will bring it up. Again this is a different model number than what was on the package of the unit I bought YET it looks exactly like what I bought. Go figure.
You know ... I'm starting to think that the website swapped the pictures and is therefore in error. So I'm pretty sure you will get the right item if you follow my original initial link.