Sonic, this is one of the few times (or the first?) I agree with Mr. T.
'Tube sound' means different things to different people. The vast majority refer to 'tube sound' as the coloration caused by a tube amp - speaker mismatch, hence the comments of 'tubby or loose bass', 'attenuated highs' etc. etc. associated with tube amps.
A good tube amplifier mated with the correct speaker will produce very solid bass and extended highs. Unlike a good transistor amp, the notes throughout the frequency spectrum will decay naturally as a tube amp has a much lower sound floor than a comparable transistor amp. Transistor amps tend to chop off the decaying notes.
Either way, no transistor amp can ever have tube sound.
Regards
Paul