Dear Guma15;
As most things in this hobby its the question of the budget. The rail (internal) four fuses effect music in lessen degree then one main fuse. So, if you want you can get better internal fuses four times the price of one main with about 20% improvment. I did it but others may choose to invest the same money (about $120 - $150) into other tweaks. For example, vibration control devices like Acoustic Revive QR8 for about $138 set of 8 or Aurious. set of 3 (about $200 - $250) to put under the amp will do more help in improving the system's sound.
Still, if you want to install better quality rail fuses then rather good stock please note: Fast Blow, 10 AMP, 1.25" size, 250v and Furutech does not have, at the moment, fast blow fuses. So it leaves only HiFi Tuning Fuses (as far as I know). A few years ago, I also made arrangments with Cable Company for discount for Spectron users. John Pharo is salesperson to get in touch rgarding HiFi Tuning Fuses.
Thank you
Simon