6x week primer:
If you want to gain on a high frequency routine then you MUST eat enough to be gaining fat. Higher frequency alters the equation and your caloric demands increase more than linearly.
You have several options regarding your workouts.
You can either double up on your weights:
100, 100, 110, 110, 120, 120
You can either reduce increment size:
95, 100, 105, 110, 115, 120
Or you can create 2 routines, each being performed 3x weekly:
A-100, B-85, A-110, B-95, A-120, B-105
A = Pulldowns/Bench
B = Rows/Incline Bench
For smaller exercises (isolations) you may not wish to alternate and use one of the first two options of progression.
You need to progress the same absolute numbers as if you were doing 3x a week, but how you do it is up to you.
Use the same volume as you would for 3x a week, and then spread it out for 6x.
So if you were doing 2x exercise, thrice weekly..it now becomes 1x exercise 6 times per week.
Only if you DO NOT GROW do you increase the volume. This is not a guessing game or how you feel etc...gains are your barometer for volume increase.
Have a hypercaloric carb day once a week even if cutting. I like to do this on day 3 or 4. IF you're bulking, then do it on day 3 and day 6.