Are you sure you don’t have a bad adapter ?
Out of curiosity I searched and pulled up an old post from 2009 where a guy measured signals through a variety of cable lengths with and without adapters and a the difference between a six foot length of cable and two three foot lengths with a connector joining them to a total six foot length was 0.005db. Worst case with any configuration was 0.03db which was equivalent to 0.1% difference.
I have in the past set up a test with a standard cable and the same cable plugged into a series of adapters up and down for a total of five additional connections that were easy to remove quickly for a simple A/B test and it made no obvious audible difference.
Totally saves me the trouble of having to test it out myself, thanks!