You got it mixed up. The original MSI 815E Pro, is the same as the Asus CUSL2(non-C), except it has one less CNR, and one more DIMM socket, everything else is virtually the same, onboard video, Intel ICH2 southbridge(ATA100)...etc, mostly minor differences.
The 815EP Pro, is the same as the CUSL2-C, as you expected, the only difference to their respective predecessors is the i815EP chipset, both equipped with Intel southbridge ATA100.
The 815EP Pro-R, is the same as 815EP Pro, but with RAID controller and Intel southbridge ATA100. Currently, Asus does not have a counterpart to MSI 815EP Pro-R.