It was a shame that I could not go.
Headphones are headphone amplifiers. So,
BAKOON PRODUCTSのHDA-5210MK3です。
//www.exclusive-audio.jp/shop/products/detail.php?product_id=12
It is not well known in Japan, but overseas it is a fairly famous headphone amplifier for east and west.
Enjoy the overwhelming sound of current output!