Dumb Head Phone Question

Your Oppo 105 already has a pretty decent built-in headphone amplifier.

You're all set.

"Also, I would welcome any comments regarding the head phone choice."

Sennheiser is known for making headphones that are fairly laid back sounding. I haven't heard the B&W's, but if you look at their speakers, I would expect them to sound very different from the 700's. So if you're biased to a certain type of sound, you need to be careful in your selection process.

First off I will hands down go for the Sennheiser's. Why? Because that's what they do, they make headphones. B&W, they make speakers. Also, you need a headphone amp to drive these HD 700's or don't even bother. They will sound very FORGETTABLE without a great headphone amp (maybe a nice tubed one). The HD 700's have a impedance of 150 ohms and most headphone amps should work well (50 ohms is harder to drive, like planar headphones) So plan on making the plunge for a great headphone amp IMO one that costs around $500 to $1000 should pair nicely.

Matt M

Sennheiser also makes microphones, lots of 'em, so they are not a dedicated headphone company. That said, I love my Senn 600 phones. Most folks favor the darker, warmer 650 model. I have not heard the 700's. I have a very inexpensive headphone amp (120.00) which pleases me to no end.
You should check out the threads at head-fi.org. That is a "headphone only" site and there's lots of good info there. Don't get overwhelmed.