I'm a big Cary fan and must say that the 308 is not their best work. It uses 12au7's while the better newer Cary preamps use 6sn7's. They are much better sounding tubes with better frequency extensions.
If budget is a concern Cary's sister company, Audio Electronics Supply offers 2 6sn7 preamps. The AE-3 djh or signature version is the only one I would concider, and the one I own. It is absolutely staggering in sound presentation, clarity, detail, frequency extension, and soundstage. It is a high end design by David Hadd (Cary's owner and president).
I have heard it in many systems and have made many believers of the little guy. It is $1200 new direct from Cary/AES. A remote volume w/ mute is also available. It uses high end caps, plus oil caps, Kimber silver wiring, and wax impregnated transformer to dampen vibration. It does not use coupling caps in the output and hense the purity of sound. All wiring is point to point w/o circuit boards and it uses a tube rectifier instead of SS to convert AC to DC.
It only has 3 inputs and one output. It has Cary feet and Cary knobs on it and it loooks way cool. It is a baby slp98.