6A should be the least of your worries because it's not a very good reversal anyway. It doesn't have any foot invulnerability and it loses to throws.
It's just too easy to disrespect Tsubaki's pressure, and Valk gets decent damage and corner carry countering Tsubaki's 6A for example. You're probably better with some sort of stagger pressure (5A/2A stuff), because you want to do everything you can to stay on top of it and not let him get away.
Also, don't let him come to you, because if that happens, most likely you're gonna get hit. You need to keep moving using 236C, 214D, and making use of 2C where necessary.