CAL sigma tube dac's

what is the difference between tube dac's and the less expensive gamma dac?
Craig...I haven't auditioned the Gamma however I used to own a Sigma and currently own an Alpha tubed dac. My understanding of the Gamma is a dac that will somewhat upgrade a mid-fi cd player with a digital output. The Sigma and Sigma II have a single 12AX7 tube and offers an upgrade to most mid-fi cd players. The Alpha has 2 12AX7's (which I have upgraded to NOS Mullards) and substantially upgrades the sound fleshing out good detail, improved soundstaging and pretty decent musicality. CAL can upgrade this dac to 24/96 also. I was going to sell this dac last year but when I upgraded the tubes, I decided to keep it for my bedroom system. You can normally find one of these for sale here @ the Audiogon for $450-600. Considering it originally sold for $1500 and was Stereophile rated 'Class B', it's a steal for that price. No, it won't quite match up with current digital technology but if you can find one, upgrade the tubes, upgrade the power cord and use a good quality transport. You will be surprised at how good the sound is at this price level.