You are adding 1-2lbs of bodyweight EVERY week? How much protein do you take?
If this is the case (gaining weight, eating enough protein), then strength gains should be pretty decent...so long as the routine is suitable for the individual (which in your case, it's probably not).
Why hammer away on an unconventional routine, wishing and hoping for it to work? As much as it sounds great all this "your body will adapt" stuff...at the end of the day, your training should reflect how YOUR BODY responds, not the other way around.
It's a no brainer:
If there's lack of progress despite diet being adequate to gain weight on, then RECOVERY is the issue (over-compensation isn't being allowed to happen). Therefore, rest the muscle group longer before you train it (BBB is already at the high frequency end, so it's not a lack of frequency that's the problem).
Why don't you simply take more rest between training body parts? In other words, split it up more (e.g. 3 way split like push/pull/legs done 5-6 times a week).