Sony seems to be having a few issues lately with firmware releases. In a statement they have confirmed that after some users updated their FX6 to Ver. 5.00 they ran into audio issues. The issue is that when INPUT2 (audio input 2) switch is set to LINE, the audio from CH2 was producing an unintended level.
In response to this Sony has suspended the release of this firmware update.
Customers who have already updated to Ver. 5.00 can use the product normally by setting the INPUT2 (audio input 2) switch to MIC and then back to LINE.
This issue hasn’t affected all users who upgraded to Ver. 5.00, but it was serious enough that Sony decided to pull the update.
Sony goes on to say that users of the FX6 should wait for a while until a corrected version is released and that they apologize for any inconvenience.