I've read the forum posts as well as the blog of the Audial DAC designer but some of the technical information discussed are way over my head. Having been a DIYer since the 90s, I can't answer your question directly. Instead, I'll share how my
DIY nosTDA1541tube DAC evolved and the lessons I learned. Please keep in mind that I listen primarily to Red Book standard CDs. Same here.
1. The analog output section has the most significant effect on the sound of a DAC.
The
Topping D30 and XS DAC 01a share the same CS4398 DAC chip but I preferred the sound of the DAC 01a because of the tube buffer at the end of op-amps in the analog output path. When I compared the
AA DITB, Adcom GDA600, Muse TDA1543x4 and Audio GD R2R 11, I felt that the op-amp analog section in the GDA600 was limiting the potential of the BB PCM63 chip, because in spite of the limited frequency extremes due to the passive output of the Muse TDA1543x4, it sounded more organic. Likewise, I preferred the Audio GD R2R11 perhaps due to its discrete analog output section.
2. NOS (non-oversampling) reminded me of removing negative feedback from my first PP2A3 amp project in the early 90s - less compression and harshness.
While I was experimenting with NOS and rolling op-amps inside
80s Magnavox CDPs and the Chinese TDA1541 kit, I lucked into a 1st generation Arcam Delta Black Box (discrete analog section), which according to a
'89 Stereophile review, sounded a bit harsh in the top end. After bypassing the SAA7220 chip, I couldn't detect the harshness and it sounded better than any of the DACs I had.
3. I chose the TDA1541 because it was designed by the developers of the CD format. The chips are still relatively easy to find and the DAC kit boards from China are easy to procure and are affordable. Thus, others will be encouraged to DIY their DAC in pursuit of the sound they want.
That said, I hope you can give the S5 a listen in a familiar system before you commit to buying one.