New to headphone amps --- I'm wondering .....

All I can say is that I've never had an amp that compared to a dedicated headphone amp. The only amp I've heard of that could equal or best a dedicated headphone amp is a Cary SLI 80 and I've never heard one. My k702's with my old Rogue Cronus Magnum were awful. The same cans with my Schitt Lyr are amazing. You should check out Woo Audio as well.

In your case, by running from tape-out you're almost certainly creating an impedance mismatch that is rolling off your bass response big-time, and in general wreaking havoc on the net frequency response. The effect is exacerbated with headphones of lower impedance. The sound can be perceived as detailed or even "airy" this way, but it is not accurate. I've heard that result a few times, with a few different causes. If you're like me you'll tire of it and start craving a firm bass anchor to your music.

A properly engineered headphone amp will have a low enough output impedance to match with (most) headphones, and should thus yield a frequency response in keeping with the designer's intentions. Even those headphone amps with a higher output impedance (OTL tube amps) are usually voiced to end up sounding fantastic with certain headphones (e.g. many of those Singlepower amps and 300-ohm Sennheisers, or really almost anything before driven to clipping-- the Singlepowers should't sound nearly as good as they do, but they do).

In other cases, where you may have a headphone jack provided on say a $4K integrated, then you have to consider what's actually behind the headphone jack. What makes for a great line stage circuit is usually going to have too high an output impedance for most headphones...and rather than compromise the main circuit, it's common to see a crappy little opamp based headphone amp behind that jack. Even gear that boasts "discrete" headphone circuitry usually won't invest the right real estate, parts, and engineering to get it right (when headphones are an afterthought for most buyers of high-end speaker gear). Hence, a properly engineered $500 headphone amp may yield a much more pleasing result.

Now that's not to say that even most $600 headphone amps will sound particularly good, but it should be possible to find one (especially in the used market) for that price that will sound great. I think I remember buying an old used Headamp Gilmore Reference for like $650? That thing was awesome. And an old maxed-out PPA set me back a whopping $200 and can make other amps in the $1000 new range sound like garbage by comparison. If you're a gambling man, Singlepowers (with a rightfully deserved bad reputation thanks to their creator and their potential hazards) represent some of the most pleasing sounding amps around at any price (though a few do sound not so great...lots of unit-to-unit variation). That said, I'm not familiar with the newer crop of headphone amps from the last several years.

Lots of good points have been made above. I would particularly emphasize three of them, and add a fourth.

1)

02-10-14: Doggiehowser
The relative amount of power needed to drive cans (even something as difficult as a pair of Hifiman HE6) is a mere pittance compared to a regular pair of speakers so you don't have to pay for more power. Just a small amount of high quality ones.

To add some quantitative perspective, the maximum amount of power your 545s are rated to be able to handle is 0.05 watts. And in response to that maximum input power they will produce a very loud 99 db of volume. In comparison, a pair of box-type (non-planar) speakers rated at 90 db/1 watt/1 meter will require about 40 watts, or 800 times as much power, to produce the same volume at a typical listening distance of around 10 feet.

2)

02-15-14: Mulveling
In your case, by running from tape-out you're almost certainly creating an impedance mismatch ....

The tape outputs (as well as the main outputs) of your Exotik preamp are spec'd as having an output impedance of 330 ohms. That is about 10 times greater than the 32 ohm impedance of your headphones. For a line-level interface, ideally the load impedance should be at least 10 times greater than source impedance (at all audible frequencies); in this case it is 10 times less.

3)As was noted you apparently have no means of adjusting headphone volume.

4)After looking at the manual for the preamp I can't tell for sure whether or not the tape outputs are driven by a buffer stage which isolates them from the main signal path. Many and perhaps most preamps do not provide a separate buffer stage for their tape outputs, although I suspect after looking at the manual that yours does. If it does not, however, I wouldn't be surprised if applying the 32 ohm impedance of the headphones to the tape outputs adversely affects the sound you hear through your speakers (just while the headphones are connected, of course; I would not expect any damage to occur, that might affect sonics when they are not connected).

A dedicated headphone amp, connected to the tape outputs, would resolve all of those issues.

Regards,
-- Al

There is little discussion needed...get a dedicated amp for your headphones

Almarg,Are you sure the power is so low. Most of the headphone amps I know about put out around 0.5 wpc. (there is a wide range but I am suggesting this number just for scale)