I've owned the Mapleshade Double Helix plus version only. I have owned cables from Nordost and Analysis Plus, but not the models that you mention. I have no experience with the Silnote cables. IMHO the Mapleshade sound more similar to the Nordost line, which is not surprising considering that they both use silver clad copper conductors. They are both very fast, transparent and articulate, but can sound a tad on the lean side with some gear. Value wise, the Mapleshade cables represent a good bang for the buck cable. You'll get more brand recognition and easier re-sale with the Nordost, but you'll have to pay more for that privilege.
I can not see any problem running them with 6 ohm speakers or with tube integrated amps.
I can not see any problem running them with 6 ohm speakers or with tube integrated amps.