I would suggest you seriously consider a good Headphone amp for your Sennheisers . I also have HD800s and know they are a difficult load so a plug into the headphone jack of your amp won't do. I have The Luxman P- 750 u and my friend has a Pass Labs Head Amp and these are superb amps if maybe a little steep for some folk but there are so many out there and you can find one for both your pocket and your sound appreciation.
Headphone amp?
I would like to add high quality headphones to my system, which consists of a Pass Labs XA30.8 and XP-20 preamp, and SoundScience Music Vault plus speakers. Do I need a headset amp or is there some other way to use say, a pair of HD800s phones? I could in a pinch plug in to my CD player but I doubt it would be as good my amp/preamp. What would the cognoscenti suggest?