I think what you are currently on is more than enough to be honest. I used to run a similar stack years ago that was mainly Creatine, Taurine and Glutamine. Then I added BCAA after some period of time. The goal was to use ingredients to help me recover and add endurance (pre and post). The reason: so I can push myself harder and workout harder and not sacrifice or impact recovery. That said, what I am implying here is that you need to focus on experimenting in different exercise routines and formats, which would impact your metabolism and thus your caloric need (you will be eating more).
There are specific routines and recommendations for hardgainers, that I usually recommend for anyone even if they are not hardgainers. There is a good book I read in the past called "Beyond Brawn" which focuses on hardgainers.
H.I.T (High Intensity Training) Routines are great for bulking up. I also used the GVT (German Volume Training) with great results, and the 5x5x5 method as well. For bulking mass the easiest way for me was to do full body routine, utilizing HIT and focusing on power movement and heavy lifts. As for supplements, I think you have what you need. The only thing you can add, for your overall health is Fish Oil.
If you still want to add more, then Glutamine would be a great addition. L-Carnitine is also a good option too.
Good Luck