We run a similar setup, except that we have a healer channeling orange and yellow and keep both tanks available.
Is also what we do. We have a tank in the transition taunt the boss and have one tank on a regulator and the other with the boss + regulator.
Your issue with the configuration is the fact you don't have a DPS in the middle killing a regulator. There's too much burst damage for healing to keep up and going in purple and yellow your healers will be severely energy and cooldown starved.