I own both amps (well, make that owned in the case of the SEX; I sold the iron upgrade in the hopes of eventually going all-nickel, and am running a modified stock unit with C4S boards). The Crack has a speedball upgrade, 100uF Solens, a Tung-Sol 5998 variant (Chatham 2399), and a 5963 in the driver's seat (a 12AU7 variant).
Which is "better?" I'm not sure one can say. The amps sound different than each other, and there's times when I want SEX and other times when I just need some Crack. :-) The SEX amp is a sweeter sounding rig with a bigger soundstage over my HD650's, "floaty" midrange, and really fascinating micro-texture on certain instruments. It sounds like the great SET it is. The Crack, OTOH, sounds more powerful, has cleaner, taut bass, and sparkly treble. It exudes authority and accuracy, presenting more or less an exact version of what you put into it. The soundstage isn't as big as the SEX. I'd say it is the less "tubey" of the two amps, but neither are warm or bloated. There are plenty of similarities between the two setups, actually....it is the nuances that are different.
Cathode followers are inherently low in distortion, so I would expect the Crack to have less of a signature than the SEX amp, which is a normal triode amplifier run open-loop. The Crack also is OTL, and I find that transformers are responsible for a lot of an amp's flavor as well. Not sure you could go wrong with either....though I am especially interested to hear what the Smack sounds like, now that we have a third option!
