Good Morning, Sperera,
For many years, I developed T-Max sheet film in regular T-Max Developer. I had simply failed to notice the warning on the bottle. Since I was having no problem, I continued to use it and do so today. My normal dilution is 1:7 from concentrate; my normal developing time is 10 minutes for T-100 and 9 minutes for T-400, using a rotary drum. My sheet fim negatives are pristine, with no evidence at all of dichroic fogging or any other problem. I'd recommend trying the regular T-Max Developer with some non-critical negatives; if you see problems, then try the RS version. Regular T-Max can be mixed into a stock solution which is further diluted for use, but why bother? You'll just have one more bottle of chemicals to store. Mixing small amounts from concentrate, at least for the occasional user, is much more efficient, and the concentrate keeps very well.
As Chris has indicated, your fixing time is short. I fix T-Max film for at least 5 minutes (Kodak Rapid Fix) and don't worry if it ends up being 6 minutes sometimes.
Konical