A tube preamp will definitely not be as bright. Brightness is often not a frequency response error as it is caused by trace amounts of higher ordered harmonics. 0.005% can be too much! Tubes tend to make less of the higher ordered harmonics and so sound smoother/not as bright.
The room itself can make a big difference too. If its a lively room or if you have slap echo (clap your hands in the middle of the room and you'll hear it if its there), it might be difficult to tame the brightness without treating the room.
The room itself can make a big difference too. If its a lively room or if you have slap echo (clap your hands in the middle of the room and you'll hear it if its there), it might be difficult to tame the brightness without treating the room.