I would use strobes every time unless you've got really good window light - I just find it easier to know I'm in control of it and it's one less thing to have to think about when doing newborn sessions.
Lighting for the above is as follows (for all apart from the B&W, then substitute beauty dish for the octabox and remove the reflector to allow for more dramatic shadows):
Large (120cm) octabox camera left 2 - 3 feet from baby, as low as possible so angled downwards slightly and about 30 degrees from camera axis. Silver umbrella behind and right, about 4 feet from baby and 45 degrees from axis, about 5 foot high pointing down toward baby, feathering slightly so angled a little bit towards background. Large white or silver reflector camera right to just push a little light back in to the eyes and chin. I use a home-made beanbag frame which helps a lot with speed of setup and reliable positioning and background clamping.
My flashes are the older Lencarta Smartflash which are great for this as they don't push out as much power at the lower settings.
Most of the newborn stuff we do is at f/3.2 or f/3.5 (occasionally f/2.8) at 1/160sec and usually its exposed pretty well SOOC. If you're still getting too much power from the flashes I think your only option really is to add a filter to reign it in a bit.
Hope the above helps and makes sense! I must remember to do some pullback shots on the next session as they are quite useful (for me too, to see where I went wrong!).
Regards
Jim