I've posted a complete sketch requiring no messing with libraries to demonstrate the use of some new routines written from scratch to program the Si5351.  Where Pavel's library adjusts the two VCO's, this one follows Etherkit's lead by using one VCO at a fixed frequency and using the output msynth's to create three independent clocks at 1hz resolution.  The complete sketch can be found here:  https://groups.io/g/BITX20/files/KE7ER/si5351bx_0_0.ino
Hoping for at least a C- from Jack.  Does seem to work, but what the heck are all these funny numbers??

Jerry, KE7ER    Flora OR