Soundcheck,
Great info! Good to know about the 3.3v being the only voltage needed by the Pi, I didn't know that. I can just as easily feed 3.3v directly into the 3.3v pin when I power it separately.
Your power setup sounds good. I'm curious what you find comparing the iFi supply to good linears. I'm not an anti-SMPS bigot, I'm using amps with SMPSs, but most SMPSs haven't been engineered to sound good IMHO.
My current supply for the DAC/Pi combo has good diodes and a 15,000uf or so raw DC cap, 2 LT3083 regs (one set to 5v, one set to 3.3v) and about 5,000uf on the output of each. When I split the DAC and Pi, the Pi will get that supply and I'll use another with 30,000uf raw DC and a good low-noise ADM715x or TPS7A47xx reg on the output. I do plan to try it first with a 5v input, but also try later with a 3.3v input bypassing the on-board regulator.
And I just remembered that when I was poking around, I thought I saw that part of the DAC seems to be powered from the Pi 3.3v. I'll check again, but if I'm right, I'll cut that trace when I power the Pi separately and use a 3rd supply there.
I agree that LiPoFe4 might be ideal for this setup. See what people are doing over at Tir Na HiFi and also Barrows' posts about his battery-powered server on CA. Not sure whether just powering the Pi with battery by itself would be a significant step if you have good supplies for the rest or if you'd get the most from using 3 batteries, one for the Pi, one for the portion of the DAC currently powered from the Pi 3.3v, and one for the rest of the DAC.
Agree on the RCA jacks. I also had planned to replace the filter C's with PPS chip caps at some point, but in my experience, the power stuff will make a MUCH larger difference.
And of course, thanks for the alsamixer tip.
Later!
Greg in Mississippi
P.S. I'll post pix over the weekend. Also see the HiFi Berry forums, there's a post over there in a thread titled 'DAC Pro Analog Output FIlter Resistors' showing a guy powering his separately, but he hasn't said anything about that. Of course, if my poking around discovery that some of the DAC is powered by the Pi 3.3v, it may not make much of a difference until that is separated.