every characteristic of a device can be an advantage or a disadvantage depending on your initial requirments
What are the advantages/disadvantages/difference of using a solid state, discrete output stage instead of valves ( The G9 seems to fit the latter)? And what are the differences sonically?
general observations: what is available?,what does the designer have experience with?, space, temperature boundaries, marketing strategies, repair issues, parts, reliability in that implementation,
solid state: cheap, small, cool temp, easy,
tube: one power supply, distortion characteristics, input impeadance, output impeadance, nostalgia, unique types,
just to give you an idea.
in any design process, all these questions need to be asked or you will hemorage time and money fixing.
sonically, the bigger differences will be in how you implement, not what you implement. you can hear the difference in a tube/solid state power amp, but the most striking difference I can hear is in the tube microphone. the key is to not ruin the signal somewhere. then most designs can rock.