That works for me in Sonar X3. Are you changing the midi channel of controller mode before you turn knobs 2 and 3? When you press "CHAN" on the Beatstep Pro, a step button lights up red, indicating the midi channel you're using. Holding "CHAN" and pressing a different number will change the channel. Since you have drum volume mapped to channel 10, you need to press "CHAN + 10" while you're in control mode (step 10 will lhen light up red).
I think you're making things more difficult this way. Here is how i have mine;
-knob 1: CC# is default, midi channel 1 (controls volume of track 1),
-knob 2; CC# is default, midi channel 1 (controls volume of track 2),
-knob 3: CC# is default, midi channel 1 (controls volume of track 3),
Notice I've left the CC# alone and keep volume on the same channel.
Now if i want those knobs to do something else, here's how i have it;
-knob 1; CC# is default, midi channel 2 (controls pan of track 1),
-knob 2; CC# is default, midi channel 2 (controls pan of track 2),
-knob 3; CC# is default, midi channel 2 (controls pan of track 3),
to adjust pan in control mode, i just switch the BSP to midi channel 2 (by holding "CHAN + 2"). step button 2 now turns red.
I haven't changed anything in the Midi Control Center. I only use the midi learn function in my daw.