Would a mid-range 100 watt a/v receiver be enoguh to drive a Sennheiser 600 or 650?

I run my HD650's using an ASUS Xonar STX sound card and to me, they're being driven just fine.  The HD650's are 300 ohm headphones and need no more than 1 Vrms to drive them @ 103db.

Yes, most receivers drive headphones just fine. If you're shopping for a receiver, take your headphones along and give each a listen. If you don't hear any distortion or other problems, the receiver should work fine.

I wouldn't vouch on getting the most out of the HD650's with a receivers headphone jack.

 

I didn't like the receiver out for my Grado's,the HD650 would be even harder.

Yes, well, 100W will destroy the headphones quite handily. 

What? Only if you drive them from the speaker taps with a signal that used all 100 watts.... not likely. That is why they put headphone jacks on recievers...

In my limited experience, recievers can drive most things.  From the little I've run out of my Marantz, they can drive them to very loud levels at about 9  o'clock.

But I think he means drive them properly, which in that case I'm afraid to say a lot of the modern mass produced receivers don't do too good a job. Marantz ones do a decent job, but a lot of other's have a very underpowered headphone circuit.

 

I'm not to knowledgeable in the this area, but I would say look into a Marantz made one.

 

You could driver them from the speaker output like I have done in the past, but you have to really watch the volume dial.

You never know until you try it.  My Panny digital reciever headphone out is just awful!  Noisy as hell, really harsh sounding.  My squeezebox headphone out is almost as bad.  Sound quality out of my Fuze or Zune is much much better, but ofcourse they don't go loud enough.  Then dedicated headphone amps are at another level all together.

 

So, don't expect to get any great sound sound from a reciever today.  People do have good luck with vintage recievers though.

A receiver won't fry headphones. Usually, the headphone jack is fed by the main amp with resistors to drop the power. Granted, most receivers run in class AB and aren't ideal amps, but they're much better at delivering power than a portable amp.

I have a 10yr old Yamaha 6.1 channel receiver and it has a nice sounding output, though it's underpowered.

Sarcasm mate, sarcasm. I know the headphone output on receivers is (usually) stepped down or a separate circuit. Just thought it was funny the way the OP phrased his question. 

I have a $400 Yamaha 5.1 receiver.  Some headphones it handles better than others.  I'm not sure why.  Some of my experiences with it have been counterintuitive.  I wasn't impressed with how it handled my Grados but it handled the 600 ohm T1s just fine.  Go figure.