If you are not in a hurry, wait, in just a few months, the larger Master DOC's will see a redesign and price decrease, no later than September these should be available and the 9440 price drop will be substantial. We have a new pump that is much stronger so 1 will replace 2 and the design is being changed a little as well. Basically this change results in a price decrease of 20%. You really only need a 9420 and if you can't wait, the 9420 and 9440 are the same, just add a second pump, the hole for attaching the pump is already there, it is just plugged and the cost of doing it this way is also the same, so you can start with a 9420 and upgrade if you feel the need.