I always beatmatch with both tracks coming through the headphones. feels weird otherwise. hardly ever have my headphones on when making the actual transition though, coz like 90% of the tracks I play are either 128 or 130bpm and the difference between the two is pretty much exactly +/- 1.56bpm. so after I start playing the incoming track I only have to adjust the jogwheel accordingly which takes like 2 seconds, then I just take my headphones and make the transistion. doesn't always go to plan though so I whack the headphones on sometimes, and when im mixing other genres with different bpms like drum and bass or whatever I rely on them a bit more.