OK, I've had a chance to compare the MS-1's played straight out of my iPod and then through my amp.
I have to say, I was surprised at how good they sounded without an amp.
I was easily able to achieve comfortable listening levels, but bear in mind I'm not one who likes to blow my eardrums out at every sitting. What I consider to be a comfortable listening level may be too soft for you. YMMV
But there was a definite improvement when played through an amp. The main areas of improvement were dynamics and bass.
While playing without the amp, the iPod was in most cases at greater that 7/8 max volume. It should come as no surprise that the amp gave the music a little more elbow room.
I listened to Yes's "Fragile" album, and the difference was clear. the Chris Squire / Bill Bruford rhythm section was noticeably punchier with the amp. When listening to my ROIO of Porcupine Tree at the 2001 Nearfest, the drums and percussion was clearly more realistic. I could almost imagine I was there.
The bass was better controlled with an amp, more weighty, possessed more authority. Not that the bass was lean without the amp, but there was a definite improvement with one.
It was especially apparent when listening to some acoustic double bass on Douglas, Barenberg & Meyers's "Skip, Hop & Wobble" where Edgar Meyer's bass sounded much tauter and substantial. Not flabby my any means, just better.
The long and short of it is: my 4G iPod photo was able to do an admirable job of driving the MS-1's, but they sounded much better when played through my Portaphile V2^2 amp. Of course the usual caveats apply, YMMV, etc, etc...
