I regularly train boxing/kickboxing, 3-4x/wk, and would prefer not to let this go as I find it simply a great stress outlet, confidence builder, and an enjoyable social activity.

The problem I have is that I am not jacked, and I want to change that. I am making a plan to lift more frequently, and am wondering what the best way to go about this is. I attempted StrongLifts concurrently with my martial arts about a year ago, but found that my legs were effectively useless when kickboxing/boxing after I had lifted earlier that day or even up to a day or two before if I went real hard, which I believe is necessary to build mass.

Has anyone else gone through this? Is there any way to build muscle mass while still practicing very high intensity combat sports, akin to HIIT, I suppose. What program would you recommend?