"Just to make sure I'm getting you, do you mean iPod Touch directly or IPod Touch fed into an amp like the Protector or RX? My portable rig is an iTouch into a Protector. I don't feel like I lose bass response compared to my home Apogee DAC (though I lose detail, etc.). When I go straight into the iTouch then it's a huge difference. But, that's a matter of the iTouch's weak headphone amp section not DAC section. I'm wondering about upgrading to a JH16 myself, and would like to corroborate what I'm hearing. Thanks."
An iPod Touch or even my iPad, for that matter is not a quality source DAP for a JH13 or JH16, when direct connected to the headphone out. I have tested my iPad a bit last Saturday. It wasn't terrible, but the soundstage was much narrower and there was a definite upper bass hump (usually referred to as the "iPod Sound)." If you drop in a HQ LOD and amp, it improves considerably, but you still go thru a miniaturized, relatively low-grade DAC chip built into these devices. Until the GR9 transport or similar device materializes, that's the best option if you don't want to go to the HFM or iMod route.
The iPad USB-out is useful (with the optional Connection Kit), since you can hook up a USB DAC/Amp and bypass all that crap. I'm hoping that OS 4.0 in the next gen iPod Touch may allow this sort of connectivity, which would be awesome, if they were to up the storage to 128GB. I would consider that to replace the iMod, if that was possible. We'll have to see.
Just my 2 cents.