Valid points are made here, I do not disagree with them. However I am coming from a place of personal experience in a real world system that I owned.
The difference in the gain was not audible to me. Never thought to pay any attention to it though, that being said, it never called attention to itself enough so that I felt I needed to. I simply found it worked for me and enjoyed this setup for many years.
As far as bass quality, the BAT S.S. product was deeper tighter and had more slam than the VTL even when it was run in Tetrode. The other benefit that may be worthy to note is the BAT VK-500 could handle the demands of my speakers on bass heavy material much better. Both are high current designs that can drive almost any speaker but the when the peaks hit... the VTLs would blow fuses. When I set the BAT up to run the bottom end the fast blow on the MB450's stopped popping for no apparent reason.
For the what it is worth department. I am of the camp that does not particularly see any real advantage of tube vs solid state offerings. So my input does need to be taken with a grain of salt if your are a tube guy.
I have had both, absolutely loved both for their strengths and weaknesses. My experience has been, a well voiced and engineered product in either camp is enjoyable. For me it is more of the interpretation of the music that the component does vs one technology being superior to the other. Much like different conductors will not interpret the same symphonic work the same way, each bringing various nuances out of it that the other does not see. I would be hard pressed to say that Karajan's conducting is more musical than Dorati's.