The first rule in purchasing amplification and sound is to have a listen and test for yourself, before committing. Let the ears decide!
So.. I’d test the line out situation at a rehearsal and see how that goes. Just run the solid state amp clean and use the sound you know you like from the blackstar.
I’d say that would work and save you the $$ too.. A lot of ‘tube’ amps use transistors on the output side anyhow, and that’s essentially what you’d be doing with the line out set up.
Hope that helps mate, and enjoy the gigs.. you should post some video here for everyone if you can 🙂