FWIW...
I have not heard the Rowland Concerto but the Concentra II instead which I think is beautiful sounding though a little dry and in the same home, though with different speakers - B&W 802D instead of B&W N803, I heard the KW500 which to me is an amazing amp that was incredibly layered and nuanced and deserving of the high praise in the magazines.
hope this helps...
I have not heard the Rowland Concerto but the Concentra II instead which I think is beautiful sounding though a little dry and in the same home, though with different speakers - B&W 802D instead of B&W N803, I heard the KW500 which to me is an amazing amp that was incredibly layered and nuanced and deserving of the high praise in the magazines.
hope this helps...