Dragon2020Well, NOT the DX7s if you are planning to drive the Fostex with it. The Purpleheart is a dynamic headphone that has an impedance of only 25 ohms. The output impedance of this headphone amp is ~10 ohm (20 ohms balanced). This is far from the recommended gap of at least 8x (so a minimum headphone impedance of 80 ohms on a regular, unbalanced connection) between output impedance and headphone impedance of dynamic headphones (planar magnetic headphones are unaffected by output impedance). The Sony is closer, but not ideal.
If you're thinking about getting it to exclusively use as a DAC (like I am), then maybe. If you want to use it as an amp though, I would highly recommend against this unless you plan to change equipment soon.
The LCX only has an output impedance of 0.08 ohm (0.12 balanced), which is going to serve your purposes far better, in my opinion.
Dragon2020The DX7s will probably have better measurements than the LCX across the board, but the most audible aspect is going to be the output impedance. That said, the bass resonance of the Fostex is pretty weak. I wouldn't expect it to make a huge difference. For example, the Beyer T5p.2 (32Ohm) is minimally affected by a 120Ohm output impedance, according to measurements on diyaudioheaven. Unfortunately, his review of the TH-X00 mahogany doesn't include that, but as I mention above, the impedance curve is fairly flat. The Z1R has an even flatter impedance curve (reminiscent of planars, actually) and will work fine.
Measurements of the DX7 on audiosciencereview suggest the dac section is crazy good. I expect the amp side to perform like a balanced A30 (since that's what it is, more or less). It's a very capable amp, but the high output impedance can cause issues with some headphones (a problem exacerbated by balanced drive). The main headphones I would worry about are multi-driver IEMs and Focal's high end stuff.
If you're thinking about getting it to exclusively use as a DAC (like I am), then maybe. If you want to use it as an amp though, I would highly recommend against this unless you plan to change equipment soon.
The LCX only has an output impedance of 0.08 ohm (0.12 balanced), which is going to serve your purposes far better, in my opinion.
Measurements of the DX7 on audiosciencereview suggest the dac section is crazy good. I expect the amp side to perform like a balanced A30 (since that's what it is, more or less). It's a very capable amp, but the high output impedance can cause issues with some headphones (a problem exacerbated by balanced drive). The main headphones I would worry about are multi-driver IEMs and Focal's high end stuff.