ALSA: write asoundrc file to combine multiple sound cards into one virtual card

The project is to write an .asoundrc file that combines two Echo Layla 3G sound cards into one virtual device. Each soundcard has 8 analog output channels, so the virtual device should have 16 channels, with the 8 channels from the first device being the first 8 channels, and the channels from the second device being channels 9-16. Here is the info on the soundcards: [psylab@localhost ~]$ aplay -l **** List of PLAYBACK Hardware Devices **** card 0: Intel [HDA Intel], device 0: AD1984A Analog [AD1984A Analog] Subdevices: 1/1 Subdevice #0: subdevice #0 card 0: Intel [HDA Intel], device 2: AD1984A Alt Analog [AD1984A Alt Analog] Subdevices: 1/1 Subdevice #0: subdevice #0 card 1: Layla3G [Layla3G], device 0: Analog PCM [Layla3G] Subdevices: 8/8 Subdevice #0: subdevice #0 Subdevice #1: subdevice #1 Subdevice #2: subdevice #2 Subdevice #3: subdevice #3 Subdevice #4: subdevice #4 Subdevice #5: subdevice #5 Subdevice #6: subdevice #6 Subdevice #7: subdevice #7 card 1: Layla3G [Layla3G], device 1: Digital PCM [Layla3G] Subdevices: 8/8 Subdevice #0: subdevice #0 Subdevice #1: subdevice #1 Subdevice #2: subdevice #2 Subdevice #3: subdevice #3 Subdevice #4: subdevice #4 Subdevice #5: subdevice #5 Subdevice #6: subdevice #6 Subdevice #7: subdevice #7 card 2: Layla3G_1 [Layla3G], device 0: Analog PCM [Layla3G] Subdevices: 8/8 Subdevice #0: subdevice #0 Subdevice #1: subdevice #1 Subdevice #2: subdevice #2 Subdevice #3: subdevice #3 Subdevice #4: subdevice #4 Subdevice #5: subdevice #5 Subdevice #6: subdevice #6 Subdevice #7: subdevice #7 card 2: Layla3G_1 [Layla3G], device 1: Digital PCM [Layla3G] Subdevices: 8/8 Subdevice #0: subdevice #0 Subdevice #1: subdevice #1 Subdevice #2: subdevice #2 Subdevice #3: subdevice #3 Subdevice #4: subdevice #4 Subdevice #5: subdevice #5 Subdevice #6: subdevice #6 Subdevice #7: subdevice #7 [psylab@localhost ~]$ Detailed instructions on what to do to get it working and to test need to be included. I need to access the new 'device' from portaudio. I can provide any other information you need.