Hi Andrew et al,
I can see the logic of your quisk_hardware_vk6jbl.py to send the freq request to the v16.10 firmware without any multiplication (ie x4 in the HF bands), and use the v16.10 firmware's per band mul/offset settings.
What I have done is just to reverse that change, and send fixed x4 freq to set the Si570. When reading back, I just div by 4. This allows backwards compatibility with older versions of firmware without the per band mul/offset feature. This will also allow compatibility with other SDR software (non-Quisk) that has been set up with this x4 assumption.
(Even) with this x4 /4 arrangement, v16.10 firmware devices can (theorectically) still do the per band mul/offset for, say 6m or 2m, by setting different mul/offset values, as the mul/offset values need not be integers. Note that this is what I think, and I have not tested and confirmed this in practice.