This will be super easy, because in the Counting analysis report that ACBC gives you (off of the Analysis menu in the software), it reports by respondent what the BYO selections were and what the attribute level composition is of the "winning" product from the Tournament. So, just read that file into Excel, SPSS, SAS, R or whatever you use for analysis and compare the results by person.
I'm assuming you are selecting the option in the ACBC interface to include the BYO chosen concept within the choice tournament. Otherwise, you won't be able to know if the BYO concept ended up being the winner or one of the near-neighbor concepts seeded by the BYO concept.
And, the software doesn't really "calculate" what the respondent's favorite product is. The software generates using a randomized design (with balancing and optimizing code) near-neighbor product concepts that share a lot of characteristics with the BYO specified product, but systematically investigate the other levels of the attributes. Whichever product concept the respondent picks is the winning concept from the pool of near-neighbor cards is the one that will be reported the "winning concept" for the respondent.