In an attempt to create situations to defend different formations and play calls I use 5 defensive alignments. To defend the pass I use either 3 down Linemen and 4 LB's in cover, or move one LB to the line. In situations facing a team that runs a balanced attack I may move 2 or 3 LB's to the line. In run situations I will move 3 or 4 LB's up to the line to stuff the run. My LB alignment will change depending on the situation as well. I use the "blitz" sparingly, however I have experimented against sims with limited success. I recruit LB's with speed and tackling as premium qualities because they are the backbone of my defense and I rely heavily on them on pass coverage. My approach is far less technical than most because I do all my planning, ie. gameplanning, recruit plan, etc. with a paper and pen. The main reason I chose the 34 many seasons ago was its versatility and the fact that LB' are far more abundant and cheaper to recruit than any other defender.
Feel free to sitemail me to further discuss 34 defense alignment!!