Does this need a counter weight with a TD6 and 24x36 softbox?
A counterweight would not normally be used unless you're using a boom-arm, however it is recommended that you use a sandbag or two at the base to provide stability.
Don't know what a TD 6 is but we have a Profoto mono head with 36 x 60 soft box and need not counter weight
I don't know what a TD-6 is, But I use these with an Einstein Flash mounted with a Interfit Photographic 79" Octobox and have had no problems with that beast even raised up to nearly max extention. These are my favorite light stands because they're solid and have a small footprint. Good luck with your choice!