The AO4S-192 AIO provides four servo-balanced outputs to RME PCIe audio cards like the HDSP 9632 and the AIO. It provides a seamless way to get more analog outputs, giving you six total when combined with the two existing outputs on the cards.
When we upgraded our audio workstation we no longer had PCI slots, only PCIe slots. So we swapped out a PCI based Lynx Two B (6 channels of analog) card for a PCIe based RME AIO (2 channels of analog) card. The performance of the AIO have been very good and we were waiting for the AIO Pro to upgrade. However, once we discovered the AIO Pro would not longer offer the ability to add more analog outputs with expansion cards we opted to upgrade the original AIO instead. We prefer internal cards and IO versus having external boxes.
The AO4S AIO comes with a cable to connect it to the main AIO card. Simply seat it in an empty case opening and secure it close to the main AIO card as the included cable is fairly short. So it's best if the two cards are adjacent to each other. The AO4S AIO does not use a PCIe slot. It occupies the space in the PC but the the extender on the bottom of the card has no electrical connection. It's simply for stabilization and is not connecting to the PCIe bus. All the connectivity happens through the cable.
Once installed the additional outputs show up in RME's Total Mix software. The next step is to turn the additional channels on in the Hammerfall DSP settings. This is a critical step because while the channels show in Total Mix nothing will happened until the additional outputs are configured in the Hammerfall DSP settings. This is not obvious if you haven't configure your AIO card in a while
We tested the the new outputs with the exact sames cables, settings, content, mixer and studio monitors. To our ears all the outputs sound exactly the same. So now, we have 6 pristine channels to work with and we can route audio in endless ways from our PC to our mixer and back out. This is very useful for mixing multiple tracks but also for podcasting and and being able to have multiple sources mixed into our feed.
You can find the RME-AO4S-192-AIO selling for $350 new and for $200 or so used. Online retailers no longer stock the device and it drop ships from RME directly. You also may receive a unit with different colored capacitors. The boards with the blue and red capacitors appear to be the latest version.
Learn more about RME-Audio and it's lineup here.