is it better to upsample a 16 or 24 bit signal?

i currently use an msb full nelson which is connected upstream to a meridian 518 DSP. the meridian 518 can convert a 16 bit signal to a 24 bit signal and add noise shaping dither before it goes to the msb full nelson. how would the Upsampling in the msb full nelson (24 bit/ 132khz) deal with a 24 bit signal as opposed to a 16 bit one? would it still work properly or perhaps better? or should i not have the meridian change the signal to 24bits? what about the noise shaping dither? (is it a good or bad thing with the msb full nelson with the upsampling turned on)
please advise. thanks in advance.
i found some more information that may help.
The upsampling chip is a Crystal Semiconductor CS8420. Below is a link that discusses the upsampling chip in detail