MC18 improved audio bitdepth handling, but is no difference in performance (faster if anything) than MC17. A little more here:
http://yabb.jriver.com/interact/index.php?topic=80522.msg548095#msg548095
However, playing a 176 or 192 file with no re sampling should not require a lot of CPU. If you're getting stuttering, increasing buffering in Options > Audio > Output mode settings might help.
Thank you Matt, in your answer you made me think of a question about side effects having the re-sampling option in the path. Is there a difference between setting mc18, as example, for a 96khz input, selected to "no change" from selected at "96" (96 to 96)?
I'm asking this because when i eliminate re sampling, (say 44 and 88 to 96), to "no change", there is less or no stutters. The bad side of it is cracking noises at sample rate changes from hardware. There is no noise when the card sample rate stays the same for all files (all at 96 or all at 176) but stutters are back for sample rate files 176 and 192.
For buffering I usually set it at 5 sec and I checked the highest hardware buffering box. The same for pre-buffering. However I wonder what is happening if i check this box and also set the audio card buffering option to the highest level from the RME setting pannel. Two time setting??