Can I hook up a headphone amp to my integrated?

Good! The Manley has very low output impedance, and while the output impedance of the 6005 doesn’t appear to be specified I would expect it to also be fairly low. The 6005 appears to have a built-in headphone amp, BTW, and provides a headphone jack, but of course that wouldn’t make it possible to listen to records via headphones, and its sonic quality is unknown.

Yes, approaches 3 and 4 certainly make the most sense among those I listed. The choice of headphone amp would probably be driven primarily by the type of headphones you choose, as well as by how much you want to spend. I have no particular suggestions to offer, assuming you are interested in conventional dynamic headphones, as in my case I use an older pair of Stax electrostatic headphones. Those require a special purpose amplifier suitable for driving electrostatics, which is also made by Stax in my case. And Stax or other electrostatic headphones tend to be quite expensive these days.

Yes, using the LM just as a power amp (connecting to its "pre-in"), with a separate preamp driving both the LM and the headphone amp (and preferably providing a "tape output" that would be used to drive the headphone amp) is certainly a viable approach. But of course it would be more expensive than approaches 3 and 4 (unless you can find a headphone amp that would provide such a preamp function itself), and it would result in sonics that may or may not be either better or worse than those approaches.

Good luck. Regards,
-- Al

I took a look at the descriptions and specs on the GS-X, WA7 (although only the Fireflies version seems to be listed currently, that version including a DAC), and the LCD-3.

The GS-X seems quite promising, although I have no knowledge of its sonic quality. And, yes, it provides all of the functionality you would require, so you wouldn’t need a switchbox or splitters or y-adapters. You would connect the Manley to its RCA input, and you could connect the CD player to its XLR input via a simple RCA-to-XLR adapter. You could then connect its preamp output to the pre-in of the LM (which would utilize the LM just as a power amp), or alternatively you could connect its loop output to a line-in on the LM (choosing between those alternatives based on whichever sounds best). With the first alternative, though, you would have to have the headphone amp powered up in order to listen via speakers; I’m not certain but I suspect that wouldn’t be necessary with the second alternative (i.e., using the loop output).

The WA7 Fireflies doesn’t provide that kind of functionality, as you realize. And I’d also have some concern that its output power rating is spec’d at 1 watt into 32 ohms, which **might** mean that it can only deliver significantly less than 1 watt into the 110 ohm impedance of the LCD-3, for which amplifier power of 1 to 4 watts is recommended as being optimal.

Good luck. Regards,
-- Al

Thanks Al. I didn't realize the GS-X was $2800. Saw $699 but that was only for 1/4?  Odd way to advertise. Would you do me a favor?  Can you look at the specs for the Woo Audio WA-2 and WA-22?  Those seem to also be preamps with headphone output and 4 line in inputs and cheaper than HeadAmp. Wondering your thoughts on those.  

Both the WA2 and the WA22 have very high 100K input impedances, so in that respect they would be good candidates for approaches 3 and 4 that I had defined. As you’ve most likely seen, the WA2 also provides switching among multiple unbalanced sources, so it would be suitable for approach 4 (no switchbox). I’m not sure that the WA22 would be suitable for approach 4, because it’s not clear if the selection it provides between its unbalanced input and its balanced input keeps those inputs fully independent (i.e., conceivably it may connect the signal on the RCA input directly to one of the two signal pins on the XLR connector, and just ground the other signal pin on the XLR connector when the RCA input is selected. Meaning that the unit may have been designed with the expectation that only one of the inputs would be connected).

Also, you would not be taking full advantage of the WA22’s balanced configuration, since your sources just provide unbalanced outputs. Unless, that is, you used a suitably chosen Jensen transformer (approximately $300) to convert the output of one of your sources (presumably phono) to a true balanced signal pair.

The one slight reservation I have about the WA2 is that the specs in its manual indicate that its power capability into 120 ohms (that being close to the 110 ohm impedance of the LCD-3) is 550 mw (0.55 watts), which falls short of the 1 to 4 watt rating that is stated as being "optimal" for the LCD-3. Although that isn’t a big shortfall, as 550 mw amounts to only about 2.6 db less than 1 watt. But it could conceivably be an issue on material having particularly wide dynamic range, such as some well engineered classical symphonic recordings. The WA22 is fine in that respect, btw (1600 mw into 120 ohms).

Hope that helps. Regards,
-- Al