Arcam Rpac + Bitperfect settings

Hello!I recently purchased an Arcam Rpac and use Itunes and Bitperfect.How have you set Bitperfect for best results? The output level from the computer is not maximal if the volume is not 100% before I start Bitperfect. With bitperfect started, you can not correct the volume using the computer volume control, but the original settings affect anyway. Is it possible to change so that the volume is maximum from your PC and only corrected on Rpac?Thanks in advance!