Another option is to get the standard Buchardt A500, which costs significantly less than the Signature Edition. At current exchange rates, around $3800 USD for the standard version vs $5300 USD for the Signature Edition.
The significant difference in the Signature Edition is that it uses Purifi woofer drivers for enhanced bass performance, but the standard A500 already has excellent bass.
The Signature Edition is produced in limited runs of 50, and it is currently sold out. If you wanted it, you’d have to wait for them to release a new batch or find a used pair.