iRule for three virtual servers with three sets of ports

Right. This is very similar to what we are doing. BTW, you can stack monitors up on the pool level (or pool-member level), so you are not limited to one. You can create a monitor for each application that correlates to each of the ports, say 7651, 7652, 7653, 7654, 7655, 7656. Just add the respective port in the Alias Service Port field of the monitor.