I’m in a similar situation. While the 50 ohm BNC is the ideal plug for the SuperLine, the T-Kable on my LP12 was too large to fit it. It’s possible to get a bigger BNC, but the resistance is different, and so it’s not a recommended solution.
The RCAs on my T-Kable (an early model, from 2007) were also very tight, and I considered changing them. But after inspecting them closely, I saw that they had extremely fine slits on the sleeves, which allowed me to loosen their death grip with a needle nose pliers. They’re now snug, but not tight.
In an idle moment I looked up alternative tonearm cables, and I see that Chord will supply the Music cable with your choice of terminations. It comes in “reference” and slimline versions, the latter being suited to the LP12. The price is way beyond my budget, but this could be the ultimate for LP12/SuperLine owners. It now makes me wonder if there are any other BNC-friendly high end tonearm cables available, at more affordable prices?