Unlike the smorgasbord of options on the original I-Sonic, your listening choices on the ES2 are quite limited: either the iPod or the radio. (The third choice is any audio source you'd prefer to hook up to the auxiliary input.) The ES2 offers basic compatibility with pretty much any dockable iPod, but for the advanced features (remote control, video output), you'll need a newer model. (For a complete compatibility matrix, see this tip.) As for the radio, it delivers the standard (analog) and digital (HD Radio) flavors of AM and FM, any of which can be captured as one of 30 presets.
The alarm can be set to wake to a tone or a station preset (not the iPod). Alarm volume can be independently set, as well, so you can drift to sleep with the unit set at a soothing low volume, but have it automatically toggle up with enough power to wake you in the morning. That said, we would've liked to have seen dual alarms, not just a single. The sleep function can be set to any 15-minute increment up 90.
The Polk Audio I-Sonic ES2 is the first product to include iTunes Tagging. In theory, that feature lets you mark any song playing on an HD Radio station by pressing the "tag" key just below the LCD screen (or on the remote). Eventually, when you remove a docked iPod and resync it with your computer, you'll see a playlist under the iTunes Store tab (labeled, of course, "Tagged"). It lists the title and artist for each tagged song, and provides an easy link for more information--or to buy it on iTunes. The process works just fine--assuming the station is broadcasting an accurate data stream (not all of them do). That said, our reaction was basically "big deal." This might be really useful in a hands-free environment--such as a car--but at home, you could accomplish the same thing by leaving a pen and paper next to the radio, and just writing down songs that pique your interest. Not very high tech, to be sure, but it would get the job done just as well.
In terms of speakers and sonics, the I-Sonic ES2 is largely unchanged from the original version--and that's a good thing. It incorporates the same four-speaker design (two front, two rear) and PowerPort venting technology from the original I-Sonic. The combined result is a powerful, room-filling stereo sound with palpable bass that far exceeds what you'd expect from the I-Sonic's diminutive housing. Across a variety of genres, we liked what we heard. The jazzy strains of the Buena Vista Social Club were appropriately breathy and moody, the guitars on Creedence Clearwater Revival's familiar rockabilly beats were perfectly twangy, and the pulsing bass of Limp Bizkit's metal-charged "Nobody Loves Me" felt as if it was coming from a much larger speaker system. In fact, we'd be hard-pressed to detect any difference between the ES2's sound and that of its predecessor. Still, we were glad to see that the ES2 offers full bass and treble controls, so we could further tweak the sound to our liking.
In the end, we couldn't be more pleased with the sound quality of the Polk Audio I-Sonic ES2. But that satisfaction is tempered mightily by the product's underwhelming feature set. If the ES2 had the CD player, USB support, and network audio streaming found on the Denon S-52, the Polk system's $500 price tag would be a bit easier to swallow. Thankfully, the ES2 can fall back on its superior sound quality--it's among the best-in-class for tabletop audio systems, and easily trounces the lackluster sonics of the Denon. Indeed, discriminate listeners looking for a best-in-class iPod speaker may well find that the I-Sonic ES2 fits the bill. We only wish the features/performance trade-off didn't have to be an either/or scenario.