Wetsounds Threesome Amplifiers

I am looking to add a pair of Rev10's to my tower. I already have a Rev410 on it.. The problem is how to power the Rev10's. The boat already has 4 amps as listed:
JL Audio XD400/4 powering 2 pair of JL Audio 7.7 components
JL Audio XD600/1 powering a pair of JL audio 10 inch free air marine subs
JL Audio XD600/1 powering a JL 10 w6 sub in a bandpass enclosure: This thing rocks.
Wetsounds Syn2 powering my Rev410. And this thing rocks.

With 4 amps I am worried about adding a 5th. Ideally I would add the Syn4 bridged to power the REV10's. The other option is to remove the Syn2 and replace with an SD6 to power the pair of REV10's and the Rev410. The concern with that is now the Rev410 has a little less going to it and I really love how it is dialed in right now. Also the SD6 is much more expensive than just buying a Syn 4.

What recommendations do you all have? Cost is definitely a huge factor so the SD6 really looks unappealing. I appreciate any and all advice. Thanks all.