anyone in UK using US plug mains?

[Confused]

bypassing the fuse of the 13A UK plug by either using US or Schuko plug, the sound is bound to improve ...

With respect, that is just your opinion, and one for which there is no objective justification as far as I know.

It's also dangerous to bypass the fuse in a UK mains power connection (the same no doubt applies elsewhere), and encouraging people to do so without considering the possible consequences seems rather irresponsible if you don't mind me saying so.

The RCCB is there ... whats the worry ?

(of course all UK plugs carry a 13A fuse) as its mandatory by the UK Electricity Board.

It's the modern view on safety, such as SIL (Safety Integrity Level) reviews and similar.  It's easy to say, 'if the electrical kit has a fault then the circuit breaker will trip and all will be well', but you then have to ask the question 'what are the chances of the circuit breaker having a fault and not tripping'.  The answer to that is that they are very reliable but do sometimes fail.  So what if the circuit breaker does fail when the electrical kit has a fault?  The answer is the fuse in the plug will blow.  OK, the chances of the kit having a fault and the circuit breaker failing is low, but it is not zero.  What are the consequences of both the kit and the circuit breaker having a fault if you do not have a fuse?  Potentially fire, resulting in casualties and death.  Low probability of it happening, but very serious consequences if it does.  I guess that's why we keep the old fashioned, simple, and very reliable fuses in the UK.  You then have to consider how the power supplies in electronic products work, typically the electronics will be taking it's power from capacitors, not direct from the mains, so as long as enough current is making it's way to keep the capacitors charged, the electronics will work as designed.   A Devialet amp, for example, will work with anything from 110v to 250v, is it going to notice the tiny amount of resistance in the fuse?  I suspect not, but having said that I have listened to Devialet amps running from mains conditioners and the result was poor, with the mains conditioners sucking the life and dynamics out of the amps and music, so there is a limit somewhere, I'm just not sure if it is at the level of the resistance of a fuse.  Clearly from 'an everything matters' approach, getting rid of the fuses can only be of benefit or at worse cause no harm, so I fully understand the desire to take this approach, to have a system where every last detail has been optimised has obvious appeal.  But as others have stated earlier in this thread, do not forget safety, get everything checked out by a professional if electrical engineering is not your thing.  It's probably a better bet than burning your house to the ground and explaining to the kids that the kittens have been burnt to death or something.