My spirit folio mixer does a pretty good job but there are various things I want my mixer to be able to do that it can't handle. A bigger mixer would do most of what I want, but with modern computers there's less and less reason to do complex computations in analog hardware. All I really need is a box with some amplifying inputs that send tracks from the mic to the laptop and some outputs that let me send mixes back out again. Then any sort of complex eq, compression, or other effects can happen in software on the laptop. So I got one:

It's a Presonus AudioBox VSL1818, with eight usable [1] inputs and eight usable outputs. It attaches to my laptop with USB. You set initial (preamp) gains on the box and then everything else you do on the laptop.

Upsides:

• More monitor channels. My analog board only has one pre-fader and one post-fader monitor output. Now I can run three monitor channels, and if I can figure out the software the hardware supports six (see below).
• Remote operation. I can set my computer up to host an ad-hoc wireless network and then running "remote" software on an ipad I can make adjustments from anywhere in the hall. Right now I have to walk back to the board every time I want to adjust something. (I haven't tried this yet [2]; maybe it won't work well or I'll hate it.)
  Update 2012-11-02: I got the 'remote' set up: seems to work well!
  Update 2012-12-21: I wrote a non-iPad remote so I could use my phone.
• Better visibility. There's a real-time pre-fader level meter for each track and graphs of the eq and compression settings. You can see better what's going on inside the mixing, which I think will help with finding problems.
• Many more settings. While I don't normally make much use of eq beyond reducing proximity effect and don't use compression at all, a lot of that is that I'm still relatively new to running sound and don't yet know how to make such adjustments well.
• It has two built in DIs and phantom power switchable for channels 1-4 and 5-8. Not quite as nice as switchable for each channel, but should let me minimize the channels that have phantom power when they don't need it. [3]
• Multitrack recording. I want to dump the raw input signals to disk so that I can listen back with the ability to turn up or down instruments. Which could potentially also be useful for creating live albums. It's supposed to be able to do this, though I've not figured out how yet.

Downsides:

• While the box seems to have no trouble with producing eight independent outputs, the software is all about treating them as four stereo pairs. For the mains, that's ok, but I don't work in situations where stereo makes sense for the monitors. I don't see a way to switch the software to use each output channel as its own channel.
• Latency, the time difference between when the musician makes the sound and when it comes out of the speaker, is unavoidably higher in digital systems than in analog ones. The latency here is 1ms, however, which is low enough that I don't hear it.
• Fragility. My analog board is pretty robust. If something broke it was unlikely to take out the whole thing, and it has been chugging along since 1994. [4] I trust the connection with the computer less, so even though it's newer equipment it's probably less reliable.
• Manipulating the controls on the analog board feels much more immediate. Sliding things around on the screen of my laptop isn't exactly awkward, but is less pleasant. I'm also more worried that my automatic responses to feedback or other problems will be limited.
• Less future proof. My old board is almost twenty years old and is still fully compatible with modern gear. In twenty years will I be able to attach this box to a computer at all? Will there be ipads still working in ten years to run the "remote" software on? My old board has through-hole soldering and is, in theory, quite repairable; I suspect if this breaks the best I can do is send it back to the manufacturer.

After I've used it for a dance or two I'll have more of an idea how much I like it. I'll definitely still bring along the analog board at first!

Update 2012-11-03: There appears to be no way to name channels. Why would they leave that out? Putting tape on my computer is going to look silly.

[1] "Usable" as in, "usable by me in situations I expect to be in". So the digital IO might be great for some people but I only care about the analog XLR and TRS (1/4") ports on the front and back.

[2] I had a terrible time last night trying to update my dad's ipad from iOS 4.2 to something more recent that would run the remote software. After syncing it and making a fresh backup the install process took forever, after which the ipad had lost all it's apps and media. Restoring from backup didn't work because it crashed, stuck on 95% done and "2 minutes left". And after the crash it no longer seemed to know about the backup. It's now running 5.1.1 but doesn't have anything it used to have installed. Argh.

[3] Phantom power is 48V, mic signals are millivolts. Momentary disconnects as cables shift can make a brief disconnect-connect, which can result in the phantom power being very briefly interpreted as a signal. Cable problems that would be inaudible under normal use can become loud crackles with phantom power. Which is why I like my current system of bringing a couple adapter boxes that provide phantom power only to instruments that need it.

[4] Though I've only had it about two years.