Here's a variety of Headphone amp suggestions from our VP Mark Cohen as of March 2017– keep in mind he has his own biases. Some units are amps only; others combine both DAC and amp. Prices in USD, and may not be accurate. This is not meant to be the Holy Grail of information; just to help point the buyer in the right direction. In no particular order.
WOO Audio WA6-SE – great tube sound if you want to be in SET heaven, not very expensive. $1200.
Pathos Aurium – Hybrid tube and solid state (MOSFET), more analytical sounding than the WOO, has great features like Gain & Balance controls and balanced in/out. $1400. Amp only, no DAC. Maybe partner this with the Matrix X-Sabre DAC ($1,099).
Burson Conductor Virtuoso DAC and headphone amps. Like the Benchmark listed below, this is a DAC/preamp/headphone amp in one box, and is sonically excellent. $1995. It will drive just about anything! And it has a really cool front panel display with remote control. Just add a power amp and speakers, and you’ve got a great home system.
SPL Phonitor 2 – has a great feature - spatial controls! Plus, 3 inputs, and balanced in/out. $2k, and can be used as a line stage preamp. I’d use this with the Audeze XC for studio mixing.
Chord Hugo TT – Excellent. Different DAC sound than others due to their own FPGA implementation. $4,500. Regular Chord Hugo and Mojo are great, too.
Audeze Deckard - Yes, we’re obviously biased, but we developed this amp after listening to everything else. It sounds really, really good, and keeps up with units costing $1K, but it's only $700. And it has a great line level preamp!
Headamp GS-X mkII. Great amp for driving the LCD4s!
Cavalli Audio – An excellent choice, but we haven’t heard the latest versions.
Matrix M-Stage HPA-3 U – a best buy at about $419. This appears to be similar to the Lehmann headphone amp from Germany. If you can’t afford to spend $700 for the Audeze Deckard, buy this.
Matrix Audio Quattro II Amp/DAC – Once again, a best buy at only $899. This is probably your best choice for a balanced output headphone amp with DAC at less than $1,000. Remember, our LCD X/XC/3/4 all come standard with the balanced cables (can be purchased separately for the LCD-2).
Benchmark DAC2 HGC – unlike many of the other units, this is a full-function analog preamp, headphone amp, and DAC. $2k.
Bryston BHA-1. Choose this if you want a better balanced output amp than the Matrix Quattro listed above. $1,395. This is also one of the few amps with a balance control (like the Pathos & SPL) – more necessary than you might think as everyone’s left and right ears are different. And this is a powerful amp for the LCD-4.
Lehmann Audio Linear – A very good sounding amp, reviewed everywhere $1100
ALO – check them out if you’re a tube fanatic and don’t want the WOO WA6-SE
Oppo BD-105 and HA-1 – Yes, we know it’s a Blu-Ray player, but it has a great DAC and headphone amp built-in! And we really like the HA-1 amp/DAC – good product!
Norma Audio – Very good, and has DAC and line level preamp.
RME ADI-2 PRO. A very flexible DAC/ADC/amp with loads of DSP options. It's very clean and powerful and bats way above its $1999 price tag.
Schiit Mjolnir – If you can pronounce the name, then this is a very good balanced amp. $749 direct from them.
Audiovalve Luminare – Excellent, especially if you have both high and low impedance headphones and/or Stax Electrostatics. No DAC. About 3,000 Euros.
Portable battery powered headphone amp+DAC
Sony PHA-3 – Excellent (ESS Sabre 9018 DAC), AND balanced outputs! $995
Sony PHA-2 – Very good, if you can’t afford the PHA-3 – does DSD. $500
Others we’ve “heard through the grapevine” are good but we have no direct experience:
Ayre Codex - headphone amp/DAC $1500 with balanced outputs
Luxman P700u $$$$