Webnick, are you sure you meant to say "passive" preamp, not linestage? The two are different (though not mutually exclusive) things. You probably know this, but "linestage" just means there's no phono pre-preamplification included. "Passive" means the inputs and outputs are not actively impedance-buffered and the 'preamp' offers no gain, just attenuation. Going passive *could* offer a theoretical advantage in ultimate transparency under ideal conditions, but there's the rub - it can be very condition-sensitive. I'm guessing that for a relatively non-tweaky audiophile and bass-enthusiast like you seem to be, an active linestage preamp might be the safer bet, especially if you listen at a wide range of volumes.
(My presumptive description of you as a listener and audiophile - if correct - could also point towards SS power amplification over tubes, which generally won't give quite the bass or carefree operation that SS can. This is why many audiophiles who want to incorporate some tubes go the tubed preamp route, but that's another kettle of fish, and as a tube-lover myself I don't want to discourage tubed experimentation. In any case though, you should be able to improve greatly on the Adcom stack, whether you go all-tubed, all-SS, or a combination of the two.)
For your proposed combination of SS preamplification and tubed power amplification, I've found this can work very well, provided of course the gear is up to snuff. In particular, forgoing tubes in the preamp can eliminate some potential hassles with tube noise and finding decent tubes, while I feel that a tubed power amp is the main contributor to providing the greatest traditional strengths of tubes (as well as some weaknesses, but in areas I don't value as highly; I should note that this assessment is probably a minority view). Impedance concerns won't be a factor here: SS preamps (active ones, that is) have low output impedances and tube amps have high input impedances, so the minimum 10X ratio differential rule of thumb will be handily exceeded and no roll-offs will occur. Your options are pretty wide-open, but the way I'd approach it personally would be to get your speakers first, then find an amp that works well with them and your room and tastes, and save the preamp for the crowning touch (well, relatively speaking...next you'll start itching about your source, cables, power... :-)
(My presumptive description of you as a listener and audiophile - if correct - could also point towards SS power amplification over tubes, which generally won't give quite the bass or carefree operation that SS can. This is why many audiophiles who want to incorporate some tubes go the tubed preamp route, but that's another kettle of fish, and as a tube-lover myself I don't want to discourage tubed experimentation. In any case though, you should be able to improve greatly on the Adcom stack, whether you go all-tubed, all-SS, or a combination of the two.)
For your proposed combination of SS preamplification and tubed power amplification, I've found this can work very well, provided of course the gear is up to snuff. In particular, forgoing tubes in the preamp can eliminate some potential hassles with tube noise and finding decent tubes, while I feel that a tubed power amp is the main contributor to providing the greatest traditional strengths of tubes (as well as some weaknesses, but in areas I don't value as highly; I should note that this assessment is probably a minority view). Impedance concerns won't be a factor here: SS preamps (active ones, that is) have low output impedances and tube amps have high input impedances, so the minimum 10X ratio differential rule of thumb will be handily exceeded and no roll-offs will occur. Your options are pretty wide-open, but the way I'd approach it personally would be to get your speakers first, then find an amp that works well with them and your room and tastes, and save the preamp for the crowning touch (well, relatively speaking...next you'll start itching about your source, cables, power... :-)