With Yoga practices pranayama comes first since it prepares the body (energy wise) for meditation. Yogani uses the analogy of pranayama ploughing the field so it ready for planting the seeds (meditation). To use that analogy further, it doesn't make sense to first plant the seeds and then plough the field.
Is there any particular reason why you would do it the other way around? If not, I would stick to SBP first, followed by DM.
When I do pranayam first there is more effort. If i meditate first the effortlessness and silence is brought to the pranayam making it much more enjoyable and powerful.
why not do a pranayama sandwich? Do a short meditation first, then pranayama followed by a full meditation practice. That should work and certainly no harm in it.