The build of the SGL is very poor for a TOTL headphone let alone at this price point. The cable is covered in a nylon material that causes microphonics and the length of the pins for some reason were not measured correctly for stax pro so a plastic spacer has been placed on it (otherwise the pin would be exposed at the end and pose a lethal threat to someone who accidently touched it while it was still plugged in). The cable is also very prone to tangle and shorter than standard (4ft maybe?). The rest of the SGL is near identical build to the he1000 $1,400~ headphone, which was already cheaply built for that price point. A lot of it is clear money grab too, like the pads are essentially the same as the he1000's, which sell for $70~, but a replacement set for the SGL is $210 at 300% higher. Additionally there have been cases of distortion, specifically in the 16-20khz range that is human audible for younger listeners, and a case of mold growing on the driver. Its possible the mold is specific to that one person's environment being very humid, but it indicates the drivers could be exposed to the elements more so than other estats.
The X9k on the other hand, is extremely well built, but some units have developed driver imbalance - although they are less commonly reported now, so it seems Stax may have made a change to their assemblage to handle this. The first unit I got had channel imbalance show up within 24 hours, and my replacement unit never had issues after 6mo+ ownership. Stax has a similar issue with the first run of the sr-009 and then quietly corrected their manufacturing to deal with what was eventually decided was a problem with how the wires were soldered.
