Finally i can post something here which have revolutionalized, atleast my world:
I found that Logic Vocal Transformer plug-in is AMAZING for pitch-correcting and pitching brass instruments
but i am NOT talking about using it's Pitch parameter on the far left but by using the Robotize function; setting the 'Tracking' to 100% retains the original pitch of the recording while increasing it beyond pitches it down.
0% "robotizes" it and negative values reverses its original pitch-bends.
As i can't get hold of a Tuba/Sousaphone, simply using the Formant parameter on the far right of the plug-in does an excellent job of turning my Barritone Horn/Trombone into one.
I have tried Ableton Live's Complex Pro feature and other real-time pitch-shifters i can think of but Logic's Vocal Transformer beats them all with a clear margin!