Hiya,
Haven't posted in a very long while, but I wanted to pass along a potential solution for you that I just implemented and I'm loving it. I'm a stickler for staying as portable as possible and for a long time only carried the Touch and my headphones with me. Last month I was looking for a way to improve the SQ of my iPod Touch (Most recently the 4g) and I stumbled across these items;
Fiio E5 portable amp
- It's been reviewed a ton on the boards, but for portability, it is king. I really, really like it.
Sendstation PocketDock Line Out Mini USB Adapter
- Not only a line out, but a Mini USB adapter so that it can charge via standard USB.
Both for under $50 USD, and extremely portable. (and versatile)
Used with my Sennheiser IE6's (Soon to be IE8's), it's a pretty killer combination that (IMHO) improves the sound quality quite a bit.
I also tested this setup with my SE530's, TF10's and my Sennheiser MX980 earbuds. All performed beautifully with this setup.
Just thought I'd provide a nice option for those looking for portability and true line out capability with an iPod Touch 4G.
Kraig