Good points there. Schitt audio is very good. I too have some high end DACs that don't need optical sources, such as my PS Audio Perfectwave DAC Mk2. My only Schitt Audio DAC is the low end MODI 24/96 USB DAC, but the PSA DAC is phenomenal (and cost $4K).
I love several of my CEntrance DACs such as the MiniDAC, DACport and DACport HD, HiFi-M8 and BlueDAC, all outstanding.
The CEntrance portable BlueDAC rivals the sound quality of DAC's costing 3-4x its price, and can work via USB with Macs, and with an iPhone via USB and camera connection kit, with Android USB out, or via BT with upsampling and re-clocking to eliminate jitter (32/384 and DSD).
https://darko.audio/2017/11/bluetooth-monday-with-centrances-portable-bluedac/ The wireless sound quality rivals the wired sound quality of many other small DACs, but it doesn't have optical output like their HiFi-M8.
The HiFi-M8 was/is a fantastic portable DAC that can take input from the iPhone digital lightning port and convert it to optical out or analog headphone out (balanced and single ended), and the headphone out is clean enough to use as a pre-amp to drive a full size amp. It can also drive most full size headphones. It also works with USB input from a PC or Android as well.
I have several older Nuforce DAC's (portable micro-dac aka uDAC, and the D100 full size, and transportable HDP and Icon for desktop) that are fairly good for the price, but they were eaten up by Optima. The uDACs work via USB input and output both analog and coaxial digital S/PDIF output - with a 24/96 DAC built-in for analog out, while throwing in a decent headphone output in the deal.
The Audioengine DACs are also good sounding for the price, with a noticeable bump from the D1 to the D3, although The D1 can take optical inputs while powered by any USB, or can use USB for data.
The Audioengine D2 wireless DAC is miraculous, and has an optical output that is significantly better in low jitter than the Airport Express, in side by side A-B comparisons. Not all optical out are equal. It also can take optical or USB input for audio. The Airport Express optical out jitter may be almost as bad as the 1st Gen ATV, while the Audioengine D2 wireless optical out is indistinguishable from many wired DACs and sounds as good as the optical output of my 4 yr old MacBook Pro (it uses a 2.4Ghz Wi-Fi peer to peer network, and you can have one transmitter paired with several receivers).
One of my best portable DACs is the HiFiMan R2R 2000, which is a USB-C DAC with a desktop class DAC balanced chip about the size of a pack of cigarettes, but also has an upsampling and oversampling BT DAC that accepts AAC BT or SHDC protocol, with single ended and balanced analog outputs. A bonus is that it can read music from a microSD card and eliminate the need for a computer or phone as transport. Even the BT AAC sound quality is outstanding - I don't know how they do it.
https://hometheaterhifi.com/reviews/dac/hifiman-r2r2000-hd-streaming-audio-device-dac/