I currently have a xbox 360 with a hd dvd drive attachment. I know right now the new audio formats on hd dvd dont work, they get decoded as dolby digital plus. If i get the new xbox 360 with hdmi, will i be able to decode TrueHD or able to do lossless audio like ps3.

No.

Best sound output you can get from the HDDVD addon is 1.5mbs DTS

The 360 dosen't have enough audio bandwidth to process 5.1 or 7.1 THD. So it won't happen this generation.

The 360 dosen't have enough audio bandwidth to process 5.1 or 7.1 THD. So it won't happen this generation.

Do you mind providing a link to this information?

Do you mind providing a link to this information?

It was posted by amirm (MS insider) in the insiders thread on this forum. Despite the addition of HDMI, the audio path of the 360 can't handle the next generation formats. This possibly could be changed with the falcon re-design but I wouldn't count on it.

For now the best option is WMA Pro if your receiver supports it, or DTS if not.

Best sound output you can get from the HDDVD addon is 1.5mbs DTS

I haven't had a 360 for a few months now. So it does support the 1.5mbs DTS downmix now? Like I said, I lost track of that.

The 360 dosen't have enough audio bandwidth to process 5.1 or 7.1 THD. So it won't happen this generation.
This is a gross oversimplification. A better answer would be "The 360 is not designed to pass lossless audio streams over it's current hardware."

I haven't had a 360 for a few months now. So it does support the 1.5mbs DTS downmix now? Like I said, I lost track of that.

Yes, FW update now allows DTS downmix and they fixed the DRC problem with DD. As another poster pointed out, M$ maintains WMA Pro is the best quality option, but that is a little self-serving for them to say that and AFAIK, it's only an option on Pioneer receivers.

I think most people are going with DTS. I am and have been very pleased.