Heya Dogdoc.
A 75 gallon is typically 4' wide , just like my 80 gallon Oscar tank.
If you look at my signature, you can see a picture of the tank showing my filter setup.
Basically, I have the XP3 filter (great choice BTW) intake tube on the far left, then the spray bar accross the top on the top-left corner going right.
Now, when I had a HOB filter, like your AQ 110 (another good high-volume choice), I put it on the right side, sorta in the middle where the aquarium hood was notched out. Right now a use a powerhead quickfilter internal instead, but it's basically the same idea.
I let my Rena XP3 focus on large mechanical and biological filtration. My quickfilter does only fine-mechanical filtration (fine floss) and needs to be replaced more often than my rena XP floss.
In your case, I would setup the AQ 110 with a bottom sponge, a layer or two of floss (buy the roll stuff and cut it to shape, much cheaper), and then a bag of ceramic bio-disks on-top for added biological.
The nice thing about this setup is if you never need to boost your bio-filter on another tank temporarily, you can move some or all of your AQ filter bio-media to a brand new filter (or move the entire filter) and it will pre-seed your tank quite a bit.
Good luck with the MTS... I hit 16 in operation before I scaled back to the mere 9 + 1 pond I have now
