You're probably best off with a single spam mapped key.
This would call other mapped keys.
The benefit of calling other mapped keys, is that each would be separate... so if your wow keybinds were Alt + F9, Shift + F9, Ctrl + F9, Alt & Ctrl + F9 etc... each would fire off, but if they were straight keybinds each sent on the same step then wow will confuse Alt + F9, Ctrl + F9 and Alt & Ctrl + F9.

The process would be:
a) Create a mapped key, for each ability you would like to fire off.
- No Hot Key, these will be called by our "spam" mapped key.
- Right click actions > Keystroke Actions > New Keystroke Action
- Target gets set to Current Window (The spam key will tell a given target to use this ability).
- Key Combination gets set to whatever keybind you're using in game for that ability
(You can make your macros in IS Boxer, and then use Keystroke Actions > Named World of Warcraft Macro Action... rather than sending keybinds to the game... See: http://isboxer.com/wiki/Game_Helpers...?title=Special )

b) Repeat for each ability, that you'd like to fire off.

c) Create your master (spammed) mapped key.
- Easiest will be, right click on DPS 1 (in the Key Map: FTL DPS Keys) and select Make Copy.
- Edit the copy.
- Change the hot key to whatever you'll want to spam.
- Delete the "1 > All".
- Right click on Actions > Key Map Actions > New Do Mapped Key Action.
- Select the Key Map, and your first mapped key that you'd like to be called by the Spam mapped key.
- Right click on the first one and Copy Action to Clipboard.
- Then paste as many times as you have actions defined in A/B (immediately above), possibly with extras of the same action if you want to weight the odds of something firing off.

If you have multiple classes on the same team, just have the target set for each ability.
Example: Do Mapped Key > Obliterate > Target (an ATG): Frost DK
Example: Do Mapped Key > Frost Strike > Target: Frost DK
Example: Do Mapped Key > Crusader Strike > Target: Ret Paladin
Example: Do Mapped Key > Judgement > Target: Ret Paladin
Example: Do Mapped Key > Inquisition > Target: Ret Paladin
Because each of the actual abilities only fires off for Current Window, in other words is only activated by whatever target/ATG the the Spam key points to... there are no conflicts.

You can include IWT to your Melee Toons.
You could go with two steps, executing on Press or Release... and have your main ability on Step 1 and every other ability on Step 2.