The Alesis Ai3 is an inexpensive adat expander that provides eight channels of A/D/A conversion. They are out of production but run between $150 and $300 on the used market. The Ai3 is a good option for DAW users that don't require, (or can't afford), ultra high-end conversion but also don't want the bad mic pres and clocking complications of other low-cost options. The Ai3 only offers conversion and clocks to the DAW. It's simplicity is its primary appeal. Also, Black Lion Audio offers a comprehensive mod to the unit that's worth exploring.
If you're considering an Ai3, be aware that the units were labeled a couple different ways during their production span, despite their all being internally identical. For example, some units are labeled "20bit" and others "24bit". According to Black Lion, who spoke directly to Alesis about the issue, the 20bit and 24bit versions are internally identical. The distinction was made for marketing purposes. There is apparently no circuit or component difference and therefor no sonic difference. Apparently at the time the Ai3 was in production Alesis changed ownership several times and the product was eventually re-branded with the sexier "24bit" moniker.