Recommendations for PC -- for modest system --

Thanks for all the input.

Other than the concept of dedicated power for 20A line just for AV gear... what will it get me in real world performance?  

I understand one line - no shared power is better - but - if everything else is 'off' on the that shared line... would it not be the same as having a dedicated line?

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Why is DIY not a good option if I am using essentially what other DIY houses are using? Why wouldn't results be comparable? 

I will check out audio envy as an option...
 

Try Pangea. It is a budget PC from Audio Advisor. They are in my system and I feel they are worth the investment.
If you haven't already, call GIK Acoustics to get advise on improvements using acoustic panels. You may get better sound for the same cost.

HDMI cables:  cable between PC and Marantz AV7705.  First, you really want a very good video card.  The power supply and circuits on the video card actually influence the audio/video quality (like GeForce 1050 or better).  Small cheap video cards are okay, but not as good for video quality.

Probably one of the best HDMI cables I have found for the money is the older Wire World Starlight 5-2 (yes, 10+ years old) or a Starlight 6.  Make sure you get at least 2 meters (not too short).  You can find these used on ebay (anwhere from $150 to $400).  These older generation cables used a single 24awg silver-plated copper solid core conductor.  I found they provide excellent audio/video and beat out a lot of other cables.  DO NOT get the "Silver Starlight 6" or anything newer.  The newer Wire World generations use dual 2x26awg conductors and they just do not perform as well (audio not as good, video slightly washed out).  Not sure what is causing this, but I suspect it's dual/multiple conductors sending high speed pulses and having timing error between them.

If you want a new cable, the cryo-treated Neotech NEHH-4200 from Audio Sensibility is excellent for the money (not as good as the WireWorld above).  This is a 26awg silver-plated OFC copper conductor design.  Audio Sensibility is a Canadian company and it's around $78 US (plus shipping).

I tested Audioquest HDMI cables and was not impressed at all.  I auditioned a Vodka HDMI and video was okay, but audio was thin and bright.  I found out that they use very small 30awg conductors.


PC POWER CABLE:
I would avoid Pangea because it's gold-plated plugs and the copper isn't top shelf.  Look for a used Audioquest NRG-2 or NRG-4 cable and chop the ends, then put on Furutech Rhodium connectors.  You can look at other cable (Kimber PM14 for example).

Why is DIY not a good option if I am using essentially what other DIY houses are using? Why wouldn't results be comparable?

millercarbon seems to be completely against DIY and has consistently pushed Synergistic Research as a solution for any problem.  One man's opinion.  I have been doing DIY cables for 10+ years and some of my cables have beat out other more expensive manufactured cables.