Krak -

This question comes up often. All this stuff is expensive. If cost is the driving factor, the clear answer is 1 pair of XM9's. Case closed.

The more detailed answer needs to factor in a few things. XM9's will give you more mid bass. If you have no subwoofer in the system, then this is critical. You can tune the XM9's down to 80Hz, where the XM7's tune to 110HZ. If you have a decent sub in the system, then you need to start thinking, do I want 1 pair or 2 pair cosmetically on my tower. How much do I value head room-- (XM9's are a bigger enclosure). You can then decide on trade offs between going with a single pair of large XM9s versus 2 pair of XM7's.

A third view point (which I usually suggest) -- start with a single par of XM9's and then down the road (if needed), add a second pair of speakers into the system. If your powering with the harpoon amplifier then you'd be ready for a second set amplifier power wise. And to be fair, the opposite is true as well. If you dont ever want to add a second pair of tower speakers, then step out of the Harpoon amplifier and go with the 800.4 and save some bucks:

These are the configurations I'm speaking about:

800.4 + 1 pair XM7 or,
800.4 +1 pair XM9 or,
Harpoon +1 pair XM9 (leaves room to upgrade next season)
Harpoon + 2 pair XM9

Here's some more information for you. I snapped a quick picture to take a look at between the two models. the XM7 driver is on the left. You can see its a very simple traditional horn type speaker. On the right, the XM9 speaker looks very different. We did some special stuff to its design in that each part is designed from the ground up (all custom tools). People often associate it with an 8" speaker but its actually about 14" bigger than a traditional pro audio off the shelf 8. It's also lighter because its basket is built into the driver itself out of plastic. A lot of thought was put into it to make it lightweight, yet larger, than its XM7 brother. I dont mean to be talking down the XM7. It's just the XM9 is newer in a lot of ways.

2012-09-19 09.49.37.jpg
2012-09-19 09.49.15.jpg

There are some other details that make it cooler than the XM7 as well. The grills can be rotated in 360 degrees so they lineup correctly. The XM7 cannot. The logo on the back can be removed to uncover a switch that attenuates the horn high frequency so you have a subtle shift toward more of an SQ setup.

Both the XM7 and XM9 will come with the neoprene bags and also the spin mount clamps. I didn't catch what Moomba you have, but they will mount directly into the V2 tower if you have that on your boat.

To sum it up:

If head space is the primary concern. Go XM7
If sound performance is the primary objective. Go XM9

Good luck.

-Brian
Exile Audio