[LC3]

A few questions about EMI in desktop computers:
 

1. How can I estimate the significance of radiated EMI for my PC audio system? 
2. What components typically create a lot of EMI? 
3. In terms of both radiated and conducted EMI, is it reasonably possible for a modest PC build to have low enough EMI that it wouldn't be an audible issue for a good sound card?
4. Is EMI a significant consideration for a system with modest speakers and headphones (for example, Swans M50W and Sony MDR-V6)?
5. Are there any issues with case configuration (for example, upside-down motherboard mounting that puts the sound card right below a top-mounted PSU). 

 
I know an external DAC/amp sidesteps some of this EMI concern, but an internal sound card is convenient enough in some situations that I want to know more about the practical effects of EMI before I dismiss the sound card option altogether.  When I say good sound card, I'm thinking of the Claro Halo. 
 
Here are the basics of my old, energy-efficient budget system:
 
Gigabyte M-ATX motherboard (basic budget board)
AMD Athlon X2 4850e Dual-Core 2.5GHz Socket AM2 45W
Stock CPU Cooler
2GB RAM
8400 GS, maybe 512 MB (fanless)
Antec EarthWatts 380
one HDD
one DVD drive
one 80mm case fan
standard case configuration (PSU at top, sound card at bottom)
 
Would an SSD in addition to the HDD, as well as a fanless PSU, make a difference?  (I'm not considering these upgrades for EMI, but for data speed and noise reduction.)
 
Again, I'd just like to get an idea of how significant EMI really is.
 
Thanks!