TAS5766M: TAS5766M volume control options need clarification

Hi,

I have the TAS5766M successfully running on a custom board.  I'm quite confused, however, by the volume control options and registers; there seems to be a lot of missing and conflicting information.

To start with, the main left and right digital volume control registers aren't even mentioned in the main datasheet, which seems very odd to me given that this is a core audio function of the amp.  You have to go to to the SLAA653A ("PurePath™ Smart Amp for Laptops") app note for that info.  There, it shows that the volume control registers are 0x3d and 0x3e, with a top end range of 0x30 (an attenuation of 0.0dB).  Seems clear enough thus far.

Here's where my confusion begins.  When going through the register map available in the TAS5766M app in PurePath Console 3, I noticed another register which seems to be associated with volume control:

I can't find any mention of this 0x3c register in any documentation or app note.  It seem strange that it's only two bits wide.  What does it do?  In all of my register dumps from PPC3, it has been set to 0x0.

Next, the datasheet offers the following information about the volume control:

This invites all kinds of confusion.

1.) SLAA653A describes the bottom range of the volume control as -103dB (value of 0xFE).  The datasheet, above, shows it going down to -110dB.  Which is correct?  Perhaps -110dB is referring to the amount of attenuation in mute?

2.) SLAA653A describes the top range of the volume control as 0.0dB (value of 0x30), but the datasheet above shows it going to +6dB.  If that is true, how do I get that extra 6dB?  Set the register value to 0x3C?  The register map in PPC3 implies that it is acceptable to set the volume to something higher than 0x30 because the top two bits aren't greyed out, which seems to be the convention for indicating that bits are illegal:

3.) The "fixed gain block" needs clarification.  The "fixed" wording implies it can be set to either 0dB or 12dB of gain.  Is this correct?  If not, what is the step size?  What register controls it?  Is the gain block in the digital or analog domain?  I'd guess the latter, because if it's digital, then it seems like it would simply be part of the main volume control rather than an additional, independent digital volume control.

4.) Does the "fixed gain block of 0dB to 12dB" operate independently of any other volume control mechanism?  That is, if I set everything to its max value, the info above suggests that my max volume would be +18dB.  Is this correct?

I hope someone can clarify these things for me ASAP - I have a customer waiting.

Thanks,

Josh