Yup, your assumption is certainly valid in general. The Smash has a little bit higher output impedance (1.6K ohms) than the old Foreplay(1K) or the BeePre (500ohms single ended), so the one situation where you need to be careful is if the amp you want to run has a very low input impedance. This in not usually a problem with tube amps which tend to have a very high input impedance or with most solid state amps, but it might be a consideration with gainclone or Nelson Pass types designs which sometimes have a quite low input impedance. If the amp's input impedance is above 15K ohms you should be fine, and you might even be able to get away with a bit lower (say 10K) without noticing any negative effects like soft bass or HF rolloff.
The other consideration is amp sensitivity. A very sensitive amp might tend to emphasize any of the naturally occurring microphony inherent in these amazingly natural sounding directly heated type tubes. That's a design trade off that we find acceptable for all three of our current preamp kits and luckily it's not really a deal breaker. The simple and quite effective solution is to put an inline attenuator between the output of the preamp and the input of the amp, thus lowering any noise that is upstream of the sensitive amp.
I will add that I find the Smashup active load upgrade a particularly worthwhile improvement to the sonics of this kit. Gives it some additional headroom that is nice if the amp is not super sensitive.
