I had a very long answer in which I detailed what happens to 7x sets that are transferred to the 8x, but I decided on a brief answer instead.
Yes, 7x sets will transfer to the 8x. However, they are incomplete, do not take advantage of the 8x characteristics, and often contain settings that must be changed. Perhaps more importantly, they will not be sets, either, they will be User Programs. What you end up is a collection of user programs that need a lot of "tidying up" to be of use, and even then, they will almost never be as useful as user programs that are designed from the ground up.
It might be more productive to start with a thorough understanding of sets, including how to select all of the different voices, how to modify important parameters, how to combine sounds, and more. Then you can start saving your favorite settings as user programs. Or, if you don't need a lot of voice changes, the sets may satisfy your needs.
I have spent hundreds and hundreds of hours programming the 8x, 7x, 3x, and 1x, and in no case was it satisfactory, at least for me, to transfer sets from one v-accordion to another. Each has unique characteristics that make such a transfer less than ideal.
Just my thoughts....
Richard Noel