Miscellaneous Charges - part of asset

We created a Purchase order with miscellaneous charges, we then created two vouchers - a regular voucher, and a third party voucher. When interfacing with AM, we would like the miscellaneous charges (the third party voucher) to be part of the asset. I have tried testing this but the miscellaneous charges did not come over as part of the asset. Is there a way to make it come over as part of the asset?