So wiring, input and output stage are the same?
Out of curiosity I just looked at the Audiophonics version. Yes, the amplifier modules and power supply are the same.
The differences between the amplifiers are relatively minor, but they may be meaningful to some people. Regarding the Audiophonics version:
1. It has a different case. The on/off button and LED on the front are much larger. It also has heat sinks, but the amplifier modules are not directly connected to them.
2. It has both XLR and RCA inputs. The DIY only has XLR inputs.
3. It uses different speaker binding posts. They look nice.
4. It has both an input and an output trigger. The DIY only has an input trigger.
5. The amplifier modules are rotated 90 deg. and a spaced further apart vs. the DIY. This results in longer power wiring, but shorter speaker leads.
The case difference really is a matter of taste. I'm not sure whether the heat sinks do much since the amplifier modules are not connected directly to them, and the modules do not dissipate that much thermal energy anyway.
The RCA inputs are useful for someone who needs them.
Could spacing the amplifier modules farther apart change the stereo separation? Maybe. No way to tell unless somebody actually measures stereo separation on both units and compares them.
The shorter speaker leads are inconsequential in comparison to the speaker cables that likely will be used.
The output trigger could be useful for daisy chaining components. I just used 3-way splitter to run the trigger output from my miniDSP to the trigger input on each of my amplifiers, one of which is the Nilai500DIY Stereo.