Some updates...
I hooked up the iStreamer to my main system (NAD C162 preamp, NAD C272 power amp, NHT ST4 speakers, Sennheiser HD650 headphones), and it sounded wonderful there, too. An obvious improvement on a line-out dock again, and warmer and more musical than my Oppo BDP-83 SE, which has a nice DAC section.
But sound still goes choppy sometimes when playing and scrolling through the iPod's user interface at the same time. And a new problem has appeared.
Twice now, while playing one song, I've switched to another (selecting through the menu, not hitting the next track button), and the sound has cut out. The iPod was playing, but the iStreamer wasn't sending any sound to the preamp. In both cases, after unplugging the iStreamer's power cable and plugging it back in, the iStreamer resumed playing.
Maybe I have a defective unit? I'm going to see how much more it does this.
Speaking of defective, the RCA cable included is terrible. It's thin and flimsy, but I figured it's a pack-in cable, so what more should I expect? Then the first time I unplugged it, one of the RCA jacks busted, the metal bent and the plastic and metal separating. I'm consistently gentle and careful with my stuff, so I blame this 100% on the cable. Not impressive.
I wish all these little glitches would go away so that I could enjoy the iStreamer's beautiful sound in peace.