monoblocks: one dedicated line or two?

The answer to this question depends upon where the lines are comming from, and the 'quality' back at the service connection. If you have clean power to the hi-fi,(from the service connection) separating out the feeds to the amps won't necessarily improve the situation. If your existing lines are a source of noise, from RFI and grounding problems, then new feeds will help, though the front end will benifit more than the amps.
Good luck

I recently istalled 5 dedicated lines; 3 20amp and 2 30amp lines. One line for the digital front end; one for the turntable and phono preamp; one for tape deck. One 30amp line for each of my Krell 650MC's.

A dedicated line for each amp will improve dynamics and costs virtually nothing extra to install. If they have to run two lines, why not throw in a couple extra for good measure. Be certain to install hospital grade or audiophile grade sockets in the wall. They have a tighter connection. I used Romex, 10 gauge wire from the wall to my box,but some other audiophiles have mentioned a better stranded wire for audio. I can't remember the name.

when the job is complete, allow at least two days of having your equipment on for the new lines to break-in. My were harsh sounding at first, then glorious when burned in.

Best tweek there is in my mind. Much better than swapping for new equipment.

If you decide to run two lines to your amps, make sure that they are out of phase. That is, one line from each side of your service. The idea is that noise from one leg will cancel or equal 0 on the other. All components in a system are supposed to be in phase with the exception of monoblock amps.

jnovak, I didn't quite understand that. If the power to one amp is in phase and power to the other amp is opposed in phase how does that affect each amp separately? i.e. how do they cancel out?

Just built a new home using 4 dedicated 20 amp lines. 2 lines ( 1 each) for monos. and 2 other for components. Cost about $300. Works fine Using Thor Audio 30 watt tube monos'
Hope that helps.