[LAU] What audio interface to use for a Linux-powered surround preamp?

Hi,

(TL;DR: skip to "The main question...")

I'm planning a hobby project to build an all-digital surround/hi-fi
system. Regular surround/hi-fi systems convert digital input sources
to analog in the surround processor/preamp, but I want to keep the
signal in the digital domain as far as possible (by using all-digital
class D power amps, aka. "PowerDACs" [*] that convert a PCM signal to
an amplified PWM signal that is feeds the speaker directly through an
LPF. The heart of this system is an all-digital surround
processor/preamp that should do the following:

 1. Switch between multiple digital inputs. (typically from HDMI or SPDIF)

 2. Decode and/or upsample the input (if necessary) into a suitable
format, typically 96kHz or 192kHz 24-bit PCM in 8 channels (for a 7.1
system).

 3. Perform signal processing on the PCM signal, like room correction
and volume control.

 4. Output each of the 8 channels on separate digital outputs suitable
for connection to the power amp associated with each speaker.

AFAIK there are currently (very few or) zero preamps for sale that
meet the above requirements. Requirement #4 seems especially hard to
satisfy.

I'm therefore planning to build my own preamp based on the following components:

 - A HDMI switch with audio split (SPDIF) and RS-232 control.

 - A Linux computer that controls the HDMI switch, and contains the
audio processing software (e.g. a gstreamer pipeline doing the
decoding and manipulation).

 - A suitable audio interface with at least 8 digital outputs.

I believe this rig should be able to meet the above requirements.

The main question at this point is what audio interface I should
choose for the rig. Some points to consider:

 - Must work very well with Linux; bonus points if the vendor is Linux-friendly.

 - Must be able to output 8 channels of 96kHz/24bit PCM, preferably
using AES/EBU or SPDIF (as that's what most digital power amps seem to
accept as input).

 - USB, Firewire, PCI or PCI express? Which is more stable/supported?

 - Bonus points if it also has 8 analog outputs, as I want to
prototype this on an analog power amp before investing in digital
power amps.

 - Since this is still in a proof-of-concept phase, I'd like to spend
not more than about $1000 on the interface.

So far I've been browsing interfaces like:

 - MOTU 828mk3 (capable, but seems to be poorly supported by Linux)

 - RME HDSPe AES (very capable, lacks analog outputs, a bit pricey)

 - RME Multiface II + HDSPe interface card (has analog outputs, not
sure if 1 SPDIF plus 1 ADAT can give me 8 channels of digital output
in 96/24, pricey)

 - Focusrite Saffire PRO 40 (seems similar to RME Multiface II, but
cheaper. Unsure how well it is supported by Linux)

What other audio interfaces should I check out? Are there other things
I should keep in mind when picking an audio interface?

Have fun! :)

...Johan

[*]: Examples of all-digital power amps include the NAD Direct Digital
amps (M2 and C390DD), the Tact True Digital Amplification series, etc.

-- 
Johan Herland, <jherland@email-addr-hidden>
www.herland.net
_______________________________________________
Linux-audio-user mailing list
Linux-audio-user@email-addr-hidden
http://lists.linuxaudio.org/listinfo/linux-audio-user