hifinut1975,
Hi! This is Bob. I'm manager of Technical Support for NuForce. I'll try to help answer your questions the best I can.
First off:
1. so if I get the HDP now, and later add the LPS-2U/192 would I be effectively playing back 24/192 datastream?
It would seem so, but remember... you're still only playing back a "facsimile" of 24/192. Up-conversion can't recreate data that isn't in the original 16/44.1 recording. In the end it may sound a bit better (or not, we usually find "not"), but either way I wouldn't hold up too high of expectations.
Then:
2. I also plan to add the Icon Amp powering a pair of KEF Q100. Do I max out the volume setting on either the HDP and use the Icon Amp's volume to control the volume? or should it be the other way round? I assume the volume settings on the iMac should be maxed out.
Actually, that's a good question and I hear it a lot. A big part of the answer would be based on whether or not you'll also be listening to headphones via the HDP's headphone output. Let's assume for now you're not, and if so, the following answer should be reversed in order - uh... sort of.
OK, assuming you're primary concern is the fidelity coming from the KEFs, then we need to consider what we call "optimizing the gain structure" of the complete system. Headphone use or not, you always want to max out (O dBFS setting) the software volume. That way you're not dropping any bits at the bottom end of the dynamic range. That's the easy part. The rest is a bit trickier.
OK, since you likely don't have an oscilloscope handy that you can use for monitoring the output clipping point of the HDP, the only other option is to listen real closely and adjust by ear. Start out playing the best recording you have and set both the HDP and the Icon Amp volume controls to about 10 o'clock. If the sound is distorted or too loud, turn them both down by equal amounts until it sounds pretty decent. At this point you want to set the volume of the Icon Amp high enough to where you can hear the sound very clearly - maybe even a bit louder than you normally listen.
Next, turn up the HDP a bit and then directly turn down the Icon Amp until the volume is back to where it was before you turned up the HDP. The idea it to repeat this process while trying as best you can to keep the volume from the speakers as constant as possible. A cheap sound level meter from Radio Shack or such would come in real handy for this.
OK, with each cycle of HDP-UP and Icon Amp - DOWN, listen for the onset of any change in timbre of the instruments. Pay close attention to the upper midrange and high frequencies. The moment you hear any hint of added "brightness" you've hit the limit - the HDP has started to clip the input signal. Now turn the HDP back down to the previous level setting where there was no added brightness.
From that point forward, use the Icon Amp's volume control exclusively to adjust for the speaker sound level that you want to listen at and leave the HDP's volume control alone. If you run into recordings that seem to be brighter in a way that resembles what you heard during the previous procedure, just turn the HDPs volume down a tad and then that will become your new setting... until you run into another recording that is even louder. You really shouldn't have to do this more than a couple of times though as the limit is already being set to O dBFS by the computer, and that's pretty much a "brick wall" limit, seeing were talking digital signals there.
I guess if you do want to listen to headphones from the HDP too, there is an easy way not to have to screw everything up that you just went to all the trouble to adjust. Simply get a small piece of masking tape or similar, mark an arrow on it and stick it on the HDP to where the arrow points to its volume setting. That way if you have to turn the HDP down when listening to headphones, you can always go back to that mark when listening to the speakers again.
Finally:
3. lastly, I also intend to add the LPS to this setup. can I power both the Icon HDP and the Icon Amp with just one LPS-2U/192? the specs show both 4A and 1A outputs. but the HDP seems to require a 1.6A power supply? so do I still need 2 LPS? or can I really power both the HDP and Icon Amp with 1 LPS-2U?
Arghhh... that's another good one. "Technically," you should have the 1.6 amps available for the HDP, but in practice the odds are you won't need it unless you are cranking on some lower efficiency headphones. If you're using the HDP and I-Amp to drive the speakers, then you should be fine as the HDP is only sourcing current into the high input impedance of the I-Amp... which ain't much. If you're planning on getting one anyway, start with the 2U and check to see if it works. If you don't get any distortion then you're fine. If you do, then save a few $$$ and just get another 1U and you'll be good to go.
Hope this helps and have fun!
-Bob
