The meanings in English for the paired sentences are not the same, but are similar.
The "A" option in each of those chooses to emphasize one factor or reason for making the statement.
The "B" option uses "since" in the sense of "because," implying this factor or reason as having unequaled importance, among other potential factors, in making the statement.
Let's use your second example to illustrate:
2a With its high amount of fibre, this is the perfect snack for...
The snack has a high amount of fiber, and therefore is made all the better for.... The "fibre" here is one factor, but the prior sentence(s) may have highlighted its vitamin or mineral content, or perhaps it protein levels. All of these factors would be part of the "package" in promoting this snack as "perfect," and the "fibre" of this particular sentence might just be one additional item in the list. (As your example does not provide the prior context, obviously this possibility remains unconfirmed--but the potential exists.)
2b Since it has a high amount of fibre, this is the perfect snack for...
This statement is now a little stronger. Whether or not other factors have been earlier identified in the prior sentence(s), e.g. the snack's vitamins, minerals, protein, etc., the single factor of having "a high amount of fibre" is now placed as eminently responsible for making it "the perfect snack."
