LCD-2 from 2011

I'm using a custom 12AU7/FET zero feedback amp designed by a brilliant designer/technician I work with frequently. I discovered that my tube selection, an RCA Clear Top, may have had something to do with it. It's smoother with a French military Radio Technique I got from Upscale Audio.

I got a used LCD-X, 2021 version. It's a good match for a DAC I have on hand for a trial period, the Gustard R26. My older DAC, a modifed Gustard x20pro, was pretty bright, so that could have emphasized the peakiness in the LCD-2. In any case I like the X/R26 combination better. The only thing is that the LCD-X is a little rolled off on the high end, and the R26 isn't good at presenting the highest frequency details such as hall ambience. Through my speakers (Spendor S3/5) the high end of the R26 sounds better, but the imaging is not good compared to my modified x20pro. I'm trying to figure out whether I want a more extended, spacious headphone than the LCD-X, or whether I should modify the R26 in some way (perhaps a reversible mod: get a good 10 MHz clock).