Powerpath & Load balancing

if I understand correctly, you have lun saturation but you don't mention san saturation on the hba or san switch port.
giving additional bandwidth to the san path would only help if the host was waiting on disk response ffrom the aray or your san utilization was saturated.
I would think you might want to consider balancing the i/o going to the lun by spreading accross different luns (if possible) or expanding the lun with additional spindle(s) to add iops to the raid group.

I would advise to take a look at Analyzer on the array. Then you could understand more where is the saturation.
If the IO load on the lun is very heavy, then you could change the lun configuration as Jimbo suggested.

I would tend to agree that you need more info before making a change. It is possible that your host is driving more IO than the 2 HBA ports can handle, but more likely that the LUN/RAID group configuration is your bottleneck. If you don't have Analyzer (and I don't think anyone should run without it) you can still get EMC to gather performance data to analyze for you.