i have not tried plugging the m scaler into the weiss
reason being daniel weiss states that the 501 does internal clocking and upscaling input signals at 195 khz -- which was chosen by them as what they felt optimized the sound, so in effect, the weiss (like many better dacs) does internal upscaling to enable what they feel is the most ideal reconstruction filtering of the signal in the conversion process - as you probably know, the upsampling allows for the final filters to work ideally so one should be optimized to the other in the design process
maybe one rainy day this winter when i am very bored i may well try feeding the weiss with the scaler