I read through a bunch of forum posts, and they’d say to set the index of a specific snd-driver to 0, but they never mentioned how you figured out which snd-driver you were using. So, when I finally figured it out, I decided to make a quick post!

To check which kernel driver/modules your sound is using, type:
lspci -v

Scroll down to the relevant section, for me it was:
01:06.0 Multimedia audio controller: Creative Labs SB Live! EMU10k1 (rev 07)
Subsystem: Creative Labs CT4832 SBLive! Value
Flags: bus master, medium devsel, latency 64, IRQ 19
I/O ports at bc00 [size=32]
Capabilities: [dc] Power Management version 1
Kernel driver in use: snd_emu10k1

and:
03:00.1 Audio device: NVIDIA Corporation High Definition Audio Controller (rev a1)
Subsystem: ASUSTeK Computer Inc. Device 8334
Flags: bus master, fast devsel, latency 0, IRQ 18
Memory at fde7c000 (32-bit, non-prefetchable) [size=16K]
Capabilities: [60] Power Management version 3
Capabilities: [68] MSI: Enable- Count=1/1 Maskable- 64bit+
Capabilities: [78] Express Endpoint, MSI 00
Kernel driver in use: snd_hda_intel

So here you can see for my sounddriver, it’s using snd_emu10k1, and for my onboard nvidia card it was using snd_hda_intel. So with this in mind I put the following at the top of my /etc/modprobe.d/alsa-base.conf:
alias snd-card-0 snd-emu10k1
options snd-emu10k1 index=0

alias snd-card-1 snd_hda_intel
options snd_hda_intel index=1

Now my soundblaster card is the primary sound device. I only use my onboard sound for my headset for phone calls, etc. I loathe wearing headphones so I was getting tired of having my sound default through them.