Use one audio interface at a time..... you're asking for trouble to do otherwise. 


ASIO supports one device at a time. You can have your interface running on ASIO and use the computer's sound card running MME or something else to play back MP3 files..... I've done that. 

Using multiple devices is only problematic if the drivers are crappy...

(or if you do not clock the devices together properly)

...or if...

yeah...Lynx works...

otherwise you are at the mercy of some code warrior who is writing for an audio company and would rather be hacking, or at best an audio guy trying really hard to wrap his head around hashtags and compilers...

Dump the cards and buy one audio interface...just my two cents...too much of a headache and you ARE asking for trouble....good luck either way!

Hi guys getting ok results with ASIO 4 ALL and WDM its all about getting the default byte settings for the lamda right. BUT YES to all those who reccomend 1 card I agree. I used to use 2xA/P 24/96 stacked for 2 stereo insa and outs and never had a problem.Can anyone reccomend a PCI e 4+ stereo input card with 1/4 " inputs

pci-e , I'd have bought an RME AIO if they hadn't delayed it 1 year.. perhaps that has what you want..

http://www.rme-audio.de/en_products_hdspe_aio.php  Kev, spdif'ing 2 cards is problematic if different brands. as both are timing critical and in some cases / cards cause blue screens due to them going out of sync. OR it'd lose sync. had that with a few cards over the years, where using the audio instead worked better, but not so clean sounding.

What about the differences in the internal clocks of each will that cause sync issues?

FWIW, It's a PITA to try and get two different make audio interfaces to sync/operate as one.
By definition, it's not possible via ASIO.
Thus, you have to use WDM (which works well with some audio interfaces... less so with others... especially if you plan to work at ultra low latency)... AND you need to clock sync the two units (ie: via S/PDIF).
If you don't have the two units clock-synced, they will drift apart over time.  
The longer the tune, the more drift you'll experience.

One rock-solid unit that suits your needs is a FAR better option.

If they both have optical connectors you can connect them that way. The first one will simply act as a mic pre/extra input unit and the second will be the main interface doing all the work. There are limitations to this depending on how many channels you can get from the optical connection though. For example... I have a Layla Echo 3G and a focusrite Scarlett 18i6. Both have an optical connector. The echo has 8 inputs the Scarlett's ADAT connection can handle all 8 inputs at 24 bit 44.1khz but if I want a higher sample rate (like 96khz) it only allows four channels. That said even if only ONE of your interfaces has the ADAT/optical connection you could dump the one that doesn't and save money by buying a mic pre unit or a smaller interface as opposed to dumping both and buying something massive.

You could get 2 octa-captures and hook them up together. ;)

+1 on the Octa-Captures, they work. Also I believe several of the Echo interfaces can be aggregated.

WDM is the easiest option, though, by far.

BTW I'm not 100% sure of this, but I was talking to a coder from an interface company and he said there's no inherent technical reason why ASIO devices can't be aggregated, but they have unique IDs that the system expects to see...or something like that.

Who was that coder? ;)

Technically its perfectly possible to aggregate multiple asio devices into one. But there can only be one master clock device, others either clock synced to this master clock or resampled, introducing latency, jitter, quality loss, phase problems... Or they drift, resulting in buffer loss, leading from crackles to stutter and silence, depending on buffer size.