I plan to offer toslink and usb inputs and XLR balanced and RCA unbalanced outputs. This is about as much as I can pack into the back of the panel without the boards being uncomfortably close to one another.
This is the inside of the enclosure. As you can see, it's very busy! There's a 115V/230V R-core transformer, +12V and -12V bipolar AC to DC supplies, a 3.3v AC to DC supply and boards for the USB and Toslink in. The implementation is the same +12V and -12V bipolar supply to power the DC-in of the Soekris DAC and a 3.3V to power the isolated side of the Soekris, the toslink and USB modules. I also plan to add an input selector jumper to allow the end user to set the voltage that the transformer will use.
I chose DiYinHK as my source for most of the boards because they're easier to source so I don't have to rely on group buys and relatively cheap while still being excellent (this chap uses a slightly downgraded set of DiYinHK power transformers for his implementation of the Soekris). The USB to I2S is this DiYinHK XMOS-based board which is imo a step up from the Amanero or lower-end DiYinHK options most people tend to use.
I chose it despite its increased cost and size because it's isolated which means I can use the 3.3V power transformer with it and because I can cut down shipping prices because I also source the power transformers from DiYinHK. This makes it a more appealing option than the WaveIO. I also will probably use the DiYinHK Toslink to SP/DIF converter because of this same reason, but I am aware that Twisted Pair Audio have an option and I might use it in the future if I decide to borrow their input source selection board for a future revision of the DAC.
As you can see, I originally decided to go for pure single-ended outputs plus a voltage selector for the back. However, reading more about the debate between the buffered VS raw outputs of the DAC, I decided that it was worth it to get rid of the rear external voltage selector in favour of offering balanced outputs through the buffered section as well as raw unbalanced output or buffered unbalanced output (TBD). This caused some internal shuffling of the I/O boards but nothing too drastic fortunately. Here's what it used to look like: