I have got the Plinius SA-100MkIII for my Grand Pianos. Despite running the amp cold in the first 30 minutes, I can verify that the Plinius is a huge step up from the ARC D130.
Jadem6 you are right I am very happy with the upgrade. Basically everything improved. The Grand Pianos are not too laid-back as I have thought of earlier -the ARC D130 is just purely lacklustre. (Please note that this is a comparison between the SA-100MkIII and the ARC D130)
The Plinius is very airy and dynamic. With the SA-100MkIII, dynamics and transient attack were improved by leaps and bounds. More detail at the top end and the bottom end was much firmer and full compared to the wooly bass of the ARC D130. Music sounded like music now, much more lively with a greater soundstage.
Bottom-line is that the Plinius is a much better amp than the ARC D130. Okay got to get back to my listening chair now since the system has more or less warmed up after more than an hour!