SACD Player compared to SACD transport with an external DAC

Currently own a Marantz SACD Player Model # SA-14S1 purchased sometime in 2016. Have enjoyed the sound but thought I might use it as a transport and connect an external DAC to it for improved sound. I purchased a Chord Qutest DAC for another system a few years ago and tried using the Chord as an external DAC. I did an A-B comparison and the to my ears the Marantz player sounded much better. When I asked the dealer why, he responded that internal DACS are made to work synergistically with the player DAC, and would always sound better than a transport with an external DAC. I was under the impression that if I have a quality transport that I could always update my external DAC from time to time and would have virtually unlimited sound improvements. I am now looking to improve the sound of the Marantz SA-14S1, which still today sounds really good, but I thought about purchasing the Shanling Onix Zenith XST20 transport and would hook it to my Weiss DAC 204 or possibly the Meitner MA3i Dac with Meitner's network card. My other option is to purchase another SACD player such as the Marantz SACD 30 N or Marantz SACD Reference Series SACD player with USB Dac. 
In short, I was always under the impression that to maintain flexibility for future upgrades that it would be better to purchase a transport and to update the DAC as needed. Would appreciate any thoughts or suggestions.  Thank you.