They made the switch about a year ago, if I remember correctly. I have compared the Supertwo's to the ST4's and have to say I liked the ST4's the best. Here is a link to the reviews that have been posted by NHT. Pretty good stuff.
OneCall.com is currently having a sale on brand-new SuperOne for $135.00/each. I have listened to the SuperOne's replacement, the SB2, and speaking as a former SuperOne owner, the SB2 is vastly superior. The tweeter has been changed from a soft dome to an aluminum tweeter; warm sounding right out of the box. The cabinet on the SB2 is bigger than those of the SuperOne, leading to better bass response, which goes deeper and tighter. The foam surround of the AR mid/woofer on the SuperOne has now been replaced with a mid/woofer sporting rubber surround. Otherwise, same high gloss black finish.