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I really doubt they would include an "optical output" labeled "7.1 channels" if the laptop's audio could only output a 2.0 stereo signal.
Add-on sound cards have had Dolby Digital 5.1 output for over 6 years,
Desktop computers have 5.1 digital output built into the motherboard.
Why would it not be possible for a brand new laptop?
A DVD player can bitstream audio from a DVD movie disk to another device.
But the Asus Xonar U3 USB sound card would be way cheaper then a Astro Mix-amp.
Addon cards have had 5.1 output but the vast majority of it actually seems to be pass-through only. Your source audio has to be pre-encoded into DD5.1 in order for the sound card to put it out as DD5.1. For movies it's pretty straightforward, the audio is pre-encoded in DD5.1 format and the computer audio hardware simply bitstreams it through its SPDIF Port. Games do not natively generate DD5.1 signals, however, and to do that you need processing hardware and driver support, which is where audio cards come in. AFAIK, very few onboard sound solutions have realtime 5.1
encoding, and I don't know of any laptop integrated solutions. So yes, the laptop can be labeled 7.1 multichannel output by marketing but in reality it only means "7.1 multichannel bitstream or passthrough" and not true "7.1 output". The laptop itself can only generate a 2.0 stereo signal because it lacks the hardware to do the realtime multichannel encoding. Unless someone can provide an example of a laptop that has built-in DDLive!, as I am not aware of any.
Consoles all have hardware that allows realtime encoding of DD5.1 (or maybe even DTS in the case of the PS3, I don't know) content which is why you see the dedicated DH Processors like the mixamp targeted at console gamers. On the PC typically the soundcards themselves have drivers or hardware that replicates or simulates DH processing so a dedicated processor is not as necessary.
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Ruahrc: Does a soundcard need to be able to process a 5.1 or 7.1 signal, in order to pass the signal over the an external device (such as the MixAmp)?
I do agree with you that the signal itself must be 5.1 or 7.1, but that has to do with the encoding of the game or movie.
I guess the key issue is that while movies are already encoded, games are not, because you can't encode it ahead of time as the content is interactive and changing. Audio in games is processed irrespective of speaker channels or output format, being handled in an arbitrary 3D coordinate system within the game engine. It seems most modern sound cards can output 5.1/7.1 as discrete audio channels, translating the 3D sound within the game engine to 5.1/7.1 channels (although the meaning of ".1" in the LFE sense doesn't really apply here). It is also common to see audio cards being able to decode dolby digital or DTS encoded multichannel and again output that as discrete analog signals. Realtime encoding, however, is less common and you need a card that specifically lists that capability to get actual benefit from something like a mixamp. The mixamp can only decode dolby digital 5.1 sound and downmix it using dolby headphone. If you feed it a PCM stereo signal, it applies a simpler Prologic II algorithm to it in order to enhance the stereo image. If your sound card has built-in dolby headphone (or other similar) processing, then there is no need for dolby digital encoding/decoding as the dolby headphone algorithm will work directly on the 3D sound in a game at the driver level, and give you the finished output.
Dolby digital 5.1 encoded content is like putting a letter in the mail. You put it in an envelope (the encoding) to send it to another device where it is decoded (receiver takes your letter out of the envelope). To further this analogy, most integrated sound cards can only forward mail that is already in an envelope, but not put anything in an envelope and send it. Some (an increasing number) of dedicated sound cards can actually put letters into envelopes and send them out. For soundcards with DH capability, no envelope is needed, the same as if you gave a letter to someone in your house, you don't need to pack it in an envelope and send it to them, just give it to them direct.
I guess the tl:dr version is that multichannel
passthrough is very common for audio hardware these days, but has limited/no application for games.
Realtime encoding, which is the one that's more important for games, is less commonly found and and if you want to take full advantage of DH surround sound for gaming, you either need to make sure your gaming device (console or PC) can output real-time encoded 5.1 content which you then give to a decoder like the mixamp, or you have to get audio hardware (PC only) that does DH processing right on the card itself. FWIW none of the Creative cards have DH processing capability on-card AFAIK, they use their own CMSS3D system which some say is better for gaming others prefer DH. If you actually want DH and use creative hardware, you need to get one of their cards that does DDLive! encoding, which you can then pass to a DH processor like a mixamp.
Ruahrc
