6v and 3w is standard, though there are also 6v and 2.4w dynamos. In theory the 3w dynamo powers a 2.4w headlight and a 0.6w taillight, and the 2.4w one just powers a headlight, but it doesn't really matter. The rated current is produced by some specific wheel size at some specific speed, such as 12 mph, and if you go 24 mph that voltage will double. The electrical engineers at B&M understand this and they've figured out what to do about it.

So I'm a hundred percent confident your $80 B&M headlight has the circuitry to convert the variable A/C current from your dynamo hub to the reasonably steady D/C the LEDs prefer, including over-voltage etc.

I've been running a B&M lumotec cyo senso-plus premium (or some such gibberish) on my randonneuring bike for a couple years, occasionally hitting over 40 mph, and nothing has gone wrong with the light. It has an on/off switch that I never use, I just leave the light on all the time, well into the thousands of miles now.

If you want to assemble your own headlight from all the individual components, then there's a lot more to this than I can explain; but that's not the situation here so let's not worry about it.