A good solution for rear channel speakers are NHT SuperZeros, or the slightly larger NHT SuperOnes. Their overall sound balance is neutral. I think that would allow them to 'play nicely' with your Revel front speakers.
They're small & lightweight, allowing you to hang them on walls or from ceilings. They have sealed cabinets, no ports. They don't do deep bass, but that's not needed for surround speakers.
And they cost much less than a pair of S16s.
I've had a pair of SuperZeros for years, and they do the job for movies & TV. Once I hung them on the wall behind my sofa and dialed them in, I always kept them. I've replaced my front speakers with much better speakers, but I'm satisfied with those small SuperZeros as surround speakers.
NHT SuperZero
9" tall × 5" wide × 5.5" deep, 5.8 lbs.
NHT SuperOne
11.6" tall × 7.25" wide × 8.5" deep, 9.1 lbs.
Revel S16
14.75" × 13.3" × 5.5", 14 lbs.