TRX

I have always loved lifting weights, but am trying to move in a new direction and get into triathlons.  For me, lifting weights seems to increase muscle mass to a point where it might be more harmful than helpful in these events.  I bought a TRX suspension trainer and absolutly love it.  I was wondering if anyone else uses it and what they think, and what type of weight lifting you might do to supplement it?  I tend to put on mass easy and much faster than actual strength so I want to find a good balance of strength and conditioning.