They don't say SQ5, correct -- only the front ones do?
None of what you said there is correct. The R8 runs a 4 piston rear caliper with a seperate handbrake caliper, the front is an 8 piston caliper.Only the R8 has a logo on the rear - but this is because the front and rear are the same size/same part.
You may want to go and look at your R8 again then as the rears are not the same as the front.I have an R8, so you'll have to trust me i know what the brakes look like....
The ceramic fronts are actually 6 pistons not 8, but the part or plate front for all of them is the same size for both callipers.