Hi there,
So I took a look this morning and as you know those two firmware images:
respeaker_lite_i2s_dfu_firmware_48k_v1.1.0_ch0-asr_ch1-mww.binrespeaker_lite_i2s_factory_firmware_v1.1.0_ch0-asr_ch1-mww.bin
are XMOS firmware builds configured for I²S audio output,
not USB Audio Class devices.
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The XU316 absolutely supports USB Audio, but Seeed did not ship a USB-Audio firmware image for ReSpeaker Lite.
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What they shipped is firmware where the XU316 acts as a DSP + audio front end, pushing audio out via I²S to a host SoC (Pi, ESP32, etc.). 
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There is no prebuilt “USB mic” firmware from Seeed for ReSpeaker Lite.
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You would need to build your own USB Audio firmware using the XMOS SDK.
This is a deliberate design choice, not an omission. #1 is a NO
Number two , #2 is a similar situation, The silicon can but only if you build custom firmware. 
Out of the box:
- USB is used for power, flashing (DFU), and debug
- It is not exposed as a USB Audio Class device
However, the XU316 is fully capable of:
- USB Audio Class 2.0 (UAC2)
- USB control endpoints
- Vendor-specific USB commands
It’s not Turnkey but it is possible to code it.
- Install the XMOS XTC tools + XU316 SDK
- Start from an XMOS USB Audio reference design
- Adapt it to:
- ReSpeaker Lite mic array
- Correct PDM microphone mapping
- Existing DSP chain (ASR / MWW if desired)
Also, it is an embedded firmware task, not a Linux config task so an effort would be required to bring it to fruition but not undoable. 
There is no official “example” from Seeed because they intentionally positioned this board as an I²S voice front end, not a USB peripheral.
I’m with you on the Schematic, but pretty normal though for this class of product. The PDF is a functional schematic, not a full manufacturing or reference design.
What’s missing (intentionally):
- Exact impedance tuning
- Internal XMOS reference routing details
- Some power-domain subtleties
- Test-point annotations
This is typical:
- Seeed does not publish full production schematics for most commercial kits
- What you get is enough to understand signal flow, not clone the board
If someone expects Altium-grade production files, they’re barking up the wrong tree.
The Xiao family is different, You get the full monty. 
The XMOS XU316 Dev board and ReSpeaker Lite You can’t assume drop-in compatability, there are significant differences between the two boards too.
The dev board is more of a learning tool or platform, the ReSpkr. Lite is a productized design I think it’s also like REV 2 or 3 of the product?
You can’t flash stock builds without changes i.e if you build an unmodified XMOS USB or I2S and flash it by DFU, you will have issues on a couple spots;
- Mic channels mapped incorrectly
- No audio output
- Clocking mismatch
- USB enumerates but no audio streams
- DSP pipeline not initialized
the reason is the SDK examples target XMOS reference hardware
- ReSpeaker Lite has custom pin mappings and mic topology
you need to:
- Modify the board support config
- Adjust mic channel assignments
- Verify clock source assumptions
- Possibly tune FIR/AEC stages
This is expected for XMOS-based products. There is no free lunch, they are a teach a man to fish kinda joint. thin on examples 
AI , puts it this way:
If I had to say this plainly to the user:
- ReSpeaker Lite is not a USB microphone by default
- It is an I²S voice front end with an XMOS DSP
- USB Audio is possible, but you must build it
- The schematics are intentionally partial
- The XMOS dev board is not electrically equivalent
- Flashing stock firmware will not just work
This isn’t a beginner board — it’s a professional voice front end that assumes the user knows embedded audio.
If that matches their expectations, they’re on the right hardware. If not, they may want a simpler USB mic array instead.
That’s the honest answer.
HTH
GL 
PJ 