[ChartsandGrafs]

Greetings, all.  I am here because I could really use some wisdom and guidance, and judging by the expertise here, I've come to the right place.  I've recently moved into an apartment that has turned out to have some very thin walls.  My neighbors have grown tired of hearing my movies, games, and music at all hours of the night, and I've grown tired of hearing their knocking on my walls to remind me to turn it down.  
 
This state of affairs has put me in the market for a decent-quality headphone amp.  Luckily, I already have a decent set of headphones - the Sennheiser 650s.  I just need something to drive them with, as I've always found them a little bit ordinary-sounding when driven from my Onkyo home theater receiver.  I'm hoping and assuming that a nice headphone amp will help them come to life. 
 
Now, I don't know the first thing about amplifiers.  All I know is there are generally two types - solid state and tube.  I also know that a few manufacturers are held in higher regard around here than others.  But that's it.  I'm intrigued by tube amplifiers and their aesthetics, but don't have a preference.  All I need is something to drive my 650s with.  With my 650s I watch a lot of movies, play a lot of games, and listen to mostly rock, pop, and electronic music.  All of my media is stored on an HTPC, and the sound is outputted through USB to a Musical Fidelity V-Link to a Simaudio Moon 100D DAC, which is hooked up to my Onkyo receiver.  Here's my setup for the more visually inclinded:
 
HTPC -> MF V-Link -> Simaudio Moon DAC -> Onkyo HT-RC370 -> Sennheiser 650
 
As of right now, this sounds kind of "blah".   
 
How do I integrate a headphone amp into this chain of equipment?  Does it go between the DAC and the receiver?  Or is it hooked up from an output in the receiver?  Most of the headphone amps I see for sale only have connections for audio inputs, so how would I connect it to my receiver so I can listen to my loudspeakers when I wish?  I've read some product manuals but this isn't clearly explained.  It's almost as if manufacturers are selling their equipment to people who will "just know" how to hook it up.  Is there a reason I should spend more to get a headphone amplifier that acts as a preamp too?   
 
Sorry for the long post, but I really am that clueless.  
 
My budget is $1,000 U.S. dollars and under.  All of my equipment is black, so I'd prefer a black headphone amp.  Ease of use would be nice too.  Bright glowing tubes sound intriguing, but not if they are a hassle or the quality of sound is unimproved.  
 
Pretend my $1,000 is your own and pick out an amp that fits my setup.  Pretty please.          

 

[Jmstrmbn]

My first question would be have you heard headphones other than the 650s?  When I sampled them a few weeks ago I found that they were "blah" on my system as well.  They sounded great with vocals but were too smooth for me overall.  If that describes your experience with them I would consider picking up new headphones as well.  
 
To get to your main question the setup would look something like this:
 
HTPC -> MF V-Link -> Simaudio Moon DAC -> Headphone Amp -> Sennheiser 650
 
I'm not familiar with the DAC but I'm assuming that it has multiple analog outputs so you could still output to the Onkyo and any subsequent stereo/ Home Theater.
 
Now as for the Amp itself I'm not too familiar with the $1000 price range.  I can however recommend some of the more popular amps for the 650s such as the Bottlehead Crack which runs at about 450 if you don't want to build one.  On the solid state side the Burson amps are popular with the 650s and are in your price range.  I would also check out the Woo audio WA2.  This is a tube amp slightly above your price range but it has incredible reviews and is an OTL design.  The OTL design works really well with the 650s to provide a lot of current and keep them powered well.
 
*Please keep in mind I have not heard all of this gear but it should give you a place to look*
 
Also I would PM Austin Morrow, he is a forum regular and owns both a Woo audio amp and burson amp and can give you a better idea on the improvements you can expect.   

 

[Yoga Flame]

Changing amps can affect the sound of headphones, but the differences are quite subtle once you get past the basic level. Unless there's something wrong with the headphone output of your receiver, a separate amp may not deliver the kind of improvement you are looking for. It's possible that the sound signature of the HD650 just isn't for you. Or maybe the ear pads have gone flat? That does affect the sound quality significantly.
 
Still, tube amps are fun. They do impart a special sonic flavour to the sound. (Though not enough to radically transform a headphone into something it is not.) The previous poster mentioned this one, and I very much enjoy my own HD650 with the Bottlehead Crack OTL tube amp. It is usually sold as a DIY kit, but you can also fork out extra to have their technicians build it for you. And for under $1,000 I'm sure it wouldn't be hard to find someone (not me though) to build you a Crack amp + Speedball upgrade, in a custom black enclosure.
 
On the other hand, tubes may be a "hassle". They need to be replaced after many hours of use. And headphones need to be unplugged while the amp is warming up and cooling down. This can be avoided if the amp has a muting relay built in. The Crack does not have one by default, though I imagine it is possible to add one in.
 
To answer you question about connecting to the DAC, you can use a pair of RCA Y-split adapters to connect both your receiver and the headphone amp at the same time. 
 

 

[proton007]

1k is a lot of money to spend without knowing the bottleneck of your system. I recommend you try some other headphones, that will check if its the headphones that need to be changed.
Signal wise the Onkyo seems to be good.

 

[DarknightDK]

Based on what I read in your post and considering your budget of $1k for both a DAC and amp, I would recommend the following systems (in order of preference) which I consider would be an incremental step up in terms of sound quality from your current set up.
 
Systems to consider (in order of preference)
 
1) Audio Gd NFB 6 and NFB 17.2 combo (Audio gd)
2) Schiit Gungnir and Asgard combo (Schiit)
3) Audio Gd NFB-10SE (same link above)
4) Schiit Bifrost and Lyr combo (same link above)
 
Hope this helps!

 

[PurpleAngel]

The Onkyo does not have surround sound for headphones, Yamahas do.
Sell off you Onkyo and get a Yamaha RX-A700 or RX-V667, cheapest Yamahas with the better speaker amplifiers.
 
Another option is a low cost single tube headphone amplifier off eBay, ships from China.
Prices start at $50, better ones sell for $80+
 
Does your HTPC have an HDMI output, if so try running a HDMI straight from the HTPC to the Onkyo.