I currently have a 2004 SL55, but my dealer called and said that the new SL55 will have the upgraded sound and DVD NAV. So my question is, would it be pointless to sell the 04 and get the 05? and when will the 05 SL55's start to show up at the US dealers?

Depends how important the navigation system is to you. You will take a double hit, one on resale of the '04 and another on the price increase for the 2005 model. Between the two, you could be out about $15,000 (just a guess).

I hear that the new SL will arrive earlier than ususal, possibly in August.

sorry, but that would truly be a bad deal imo. it would be a lot better if you just save your money, and get a DVD nav installed for much much less, and if you want a better system get better speakers...amp, and subs...i dont see the point in upgrading to a 2005 model. GL with your decision.

Is there a way I can update the CD NAV to the DVD based Nav?

What changes are being made to the sound system for 2005?

DVD based navigation and I think it's multichannel capability for music (DVD Audio I guess).

Netstar describes the new sound system as

"Bose Audio upgraded to Audio Pilot Digital Sound with Surround Sound"

I heard they were using Harmon Kardman in the SLK. Would they use two different makers of audio at the same time?

I looked it up here is link:

AudioPilot® System

This may keep it audible (my 04 SL55 has something along these lines as I can hear it) but it won't make the sound any better. As far as I'm concerned the sound will continue to be below the level of the rest of the car. I hope I'm wrong.