First off the Pulsar clock isn’t something that the Jr can use. It’s a clock and the DS and DS Jr use a VCXO.
Tho the long term stability specs for the Pulsar a pretty good, long term stability doesn’t matter for audio (who cares if you are a second off after playing for a year…)
The near in phase noise of the Pulsar isn’t substantively different that the oscillator pack used in the DS and DS Jr (and is worse as the frequency goes up) - we didn’t cheap out on the clock. I got the lowest phase noise I could find at the time and tho people have been advertising the lowest phase noise in other DACs, they are using the lowest phase noise available in a small package. I use a bigger package so I can have even lower phase noise…
Also FWIW The Jr has a custom discretely implemented regulator used just for the clock so the power is pretty good for it as well.