>> Does anyone out there have the same level of knowledge on Mac based systems.
I thought I'd share my experience on the Mac. Thankfully, the Mac does not have as many issues to deal with, e.g., there is no kmixer which needs to be carefully jettisoned from the signal path. That said, there are still some issues.
First, let me describe my signal path.
Mac Mini -> Firewire400 -> RME FireFace400(transport only) -> SPIDF -> Grace M904 (DAC/Preamp).
Because the Grace does not output wordlock (unfortunately, it can slave only), I set the FF400 is WC Master, and run an external WC Coax to the Grace.
RME FireFace400(word clock) -> COAX -> Grace m904.
All media on the Mini was ripped in ALAC (apple lossless) format using iTunes. It is important to note, that, this is not a "bit perfect" operation as there maybe errors during the physical read of the optical media. iTunes doesn't care, it just reads the stream. To minimize this problem, but not eliminate it, select the "error checking" option in the iTunes preferences. Currently, I'm researching alternatives to iTunes for ripping. Not certain if there is a good OS X solution at the moment.
Following the instructions on the Benchmark Wiki, it is also probably a good idea to disable any EQ, Cross Fading, Normalization, and Audio Enhancement prefs in iTunes as well.
One reason I selected the RME FireFace is that it is not USB :-) Actually USB is just fine; however, most of the current crop of USB transports and DACS use chips tied to the USB 1.x standard which limits playback to 16/48 or 24/96. USB 2.x changes this, but it is rarer to find.
With FW400, 2 channel 32/192 is possible, one does not need FW800 for this. RME also implements their own FW fpga, and include their own drivers. This is a good thing, since they control "both ends of the pipe", so to speak, and use a proprietary "transport" protocol over FW. Finally, naturally, the MacMini has no PCI slots, so an internal card such as the 2496 wasn't possible, though that would have worked well.
I have spoken with RME, and they claim that the FF400 digital out is "bit perfect" and that they do not do any SRC within the unit. I have not been able to verify this directly (yet), but I have no reason to question their claim on this point.
SRC is, instead (optionally) performed by the high quality OS X system AudioConverter SRC. Between the Tiger and Leopard releases, this SRC implementation improved dramatically. It really is world class. For comparisons with other SRCs, take a close look at http://src.infinitewave.ca/ In particular, I was rather shocked to see how Weiss compared with the Leopard SRC.
One important consideration to note, is that iTunes, internally, is not doing any SRC on Leopard. SRC settings are global to any app, and owned by the physical "device", so it is important to set your transport format first within AudioMidi prefs, and then launch iTunes in that order. iTunes could register that it wants to get dynamic notifications when the transport format changes underneath it, but I don't believe it actually does this.
I have found upsampling in OS X software, to result in significant improvements in the sound. There is a rather dramatic difference between 16/441 and 32/192 - particularly w.r.t sound staging. The difference is even more significant when the FF400 is removed from the signal chain and it is compared to 24/96 MacMini -> TOSLINK -> Grace M904.
One can speculate why this is the case. Maybe there is jitter, error, or RF interference influencing the MacMini's TOSLINK out. Perhaps software upsampling "spreads out" quantization error over a wider frequency range so the Grace M904 DAC has an easier time of it, even though it is also upsampling (Mhz range). Perhaps the FF400 transport produces cleaner and, comparatively speaking, jitter free output. Perhaps I'm enjoying pleasing artifacts of the lowpass filter in the OS X SRC. Who knows.
What I do know, is that this particular setup sounds superb when I render through my biamped Lipinski L-707's with Lipinski L-301 monoblocks.
This, coupled with the convenience of FrontRow (which has an unfortunate bug, currently, where it won't display album art when streaming from a remote iTunes server), makes this an ideal setup for me. It's been well worth the effort getting there.
cheers.
Craig Hansen-Sturm