Today I finally got time to test out my new tube amp, a Audio Space Mini Galaxy I. First, the amp does make the K701 sounds much better. Before going into the amp's sound, I needed to decide my audio path setup. There are two main paths (with a small variation) that I can use:

1a) iMac optical Toslink out, to Presonus Central Station, main line out, to Mini Galaxy analog in. 1b) iMac optical Toslink out, to Presonus Central Station, cue line out, to Mini Galaxy analog in. 2) iMac USB out, to Mini Galaxy USB DAC in (it has a burr brown 2702 DAC)

Quick answer, 1b is the best.

At this point it is hard to see if the difference is due to the Toslink vs USB out on the iMac, or the DAC in the CS vs the DAC in the Mini Galaxy. But using one of my test track, track one on the Speaking In Strings CD by Nadja Salerno-Sonnenberg, the Swan, I can hear the string and her breathing much more clearly with option 1.

The reason of using the cue line out is that I can use the volume control on the CS to lower the output. On some tracks, the main line out from the CS is so loud that I can barely turn the volume on the amp pass "min".