I think that what some posters here are gleefully overlooking is that many mains disturbances are easily measurable with the right test equipment, and are easily and relatively cheaply correctable - I'm not suggesting you can always hear them, and I'm not suggesting some fancy length of mains wire will sort the problem either.
For Tonya - the last professional recording studio I was in (in the West End of London, admittedly several years ago now) I was paid to strip out and skip a rack of life-expired Yamaha professional amplifiers (one of which I kept) which were all hard wired into separate 3000kva Airlink balanced 115-0-115 volt mains units, themselves fed from a robust dedicated/ spike-suppressed 240 volt ring which had been taken directly off a separate phase of a substantial 415 volt 3-phase supply. The mixing desk and processing racks were taken off this same phase too, but all hard wired in, and definitely no evidence of cheesy £5 extension blocks there! Maybe you do things differently in Norway!
For the record, I'm split here: My hi-fi is hard wired into the mains, but uses no fancy mains cables at all because I hear no benefit. My AV system does, because I do... which kinda follows Musicraft Rick's logic. As for spikes - yes, I can measure these on my mains supply, and I treat those at source with a low-cost Isotek device. Measurement (rather than pure supposition) tells me they are being suppressed.
I think the original posters' concern was really a lack of wall sockets, where he had resorted to using mains extensions/blocks. Given he had already spent the money on a dedicated mains supply, my suggestion was simply to add more wall sockets so the OP could plug as much as possible directly into the wall and onto that same supply. If I read the above posts correctly, I think that's in keeping with both Rick and Tonya's approach too - it has nothing to do with using fancy mains cables at all.