I really like MikScrollingBattleText also and as far as I know it can display anything you like. It actually has documentation too, if you look in the addons folder.

Anyway lets see if I can describe what I did to get party damage to show up.

1. /msbt
2. I went to the scroll areas tab and made a new area called partyout. Then hit configure scroll areas and put it next to my damage.
3. Goto the Triggers tab, click on add new trigger
4. For the Output message do something like '%a %n'
Most main events allow the following substitution codes:
  • %n - The name of the source of the event.
  • %r - The name of the recipient of the event.
  • %a - The amount associated with the event.
  • %s - The skill name associated with the event.
5. Now you have a new tigger added. Click on the circle to configure the conditions.
6. Main Event should be skill damage (basically all spells)
7. Delete all the default conditions
8. Add a condition, source unit affiliation = party member. (Basically what this is saying is when the source of a spell is coming from a party member fire this trigger)
9. Save the condition changes.
10. Click the A edit the fonts the way you want.
11. Click the little screwdriver/wrench. Then I changed the Output scroll area to my new partyout box.
12. Profit?

Hopefully this all made sense.

You can also make triggers for other things, like white damage, skill misses (so you can see what party spells are being resisted).
Also I made a scroll area with PartyIn when my party members are taking damage. here the condition is recipient unit affiliation = party member.