Sennheiser is an excellent headphone, and the 600 and 650 can be had at reasonable prices.
Some headphones, like Staxx, Sennheiser and others draw a lot of power and would sound much better through a dedicated headphone amp than through the headphone jack on your Onkyo receiver. Closed back headphones will isolate the listener from the spouse's noise, or vice versa. Open headphones usually sound more natural and are the more common high end design.
But since no one else has told you, I will... Here's the thing.
Headphones are speakers. They are just small speakers for your ears. And like all speakers, they all sound VERY different.
Buying a set of headphones, based on something someone tells you or that you read, without listening to them, is like buying a painting based on a written description alone. It's madness. If you try buying headphones online, make sure you have a good return policy.
The best advice you can get is this: Find your nearest audio store that carries headphones, go, and have a listen. Choose the ones that sound best to you.