I would definitely consider the Mahlers an improvement. I've heard both, and IMHO, the Mahlers are much more musical. I've had an all BAT system driving a pair of VA Strauss, though only the VK-D5SE cd player that you mention. I believe I had the VK-50SE, VK-500 and the VK-P5 at the time as well.
If you like the BAT sound, I think you would prefer the Mahler's too.
If you like the BAT sound, I think you would prefer the Mahler's too.