Fuse upgrades? -- 6.3 amp 250v 5X20mm fast blow fuses

Another note.  I haven't tested the Synergistic BLACK/BLUE fuses. The older SR20 fuse is very clean and fast, but it lacks the high frequency response (so it sounds a little like a Class D amp would).
The Synergistic "RED" fuses is about the least offensive fuse.  It will sound okay in any system, but it is slow and not very detailed.  The Isoclean actually gave more detail and resolution, even though it was still a warm sound.

Before we have a zealot coming in and reducing this thread to a troll fight, I will say that fuses are a way to tune your sound.  There's no right answer and I have actually used different fuses in different situations to "adjust" the sound.
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Such as, Furutech are probably the most neutral high resolution fuse.  However, too many Furutech in one device can make things too warm/slow.  If you have 4 fuses in the DNA, you probably have a single "Main A/C" fuse.  I would do the 4 fuses all Furutech and then keep the stock fuse for the Main A/C or look at faster alternatives.
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Hi-Fi Tuning Supreme is a silver/gold mixture and it is a much faster sound with faster attack and more detail.  However, it can easily push a system over the line into the "too fast/bright/harsh" area. 

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Isoclean or Hi-Fi Tuning Supreme "Cu" (copper).  These are gold-plated copper and can be used to make a system warmer sounding.
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There are others you can play with, but I haven't tested any of the other new offerings.

Couple of additional thoughts.  You may not hear a difference with fuses.  Your equipment/speakers may not be high enough resolution to hear the differences.  On very warm equipment, just putting in one Hi-Fi Tuning fuse may not may any significant amount of difference (especially if there are 3 other fuses that are working in conjunction).  If you have 4 internal fuses on the DNA, I would suggest upgrading all 4 of them to get an "idea" of what a specific fuse is doing.  I suspect they are all post-transformer or post-regulator fuses (2 for each channel).

Yes, audiogon is suffering from a lot of web site errors and instability this weekend.  I usually "copy" my entire post before hitting "submit" just in case the site jinks.
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Yeah, I agree that the cheap fuses with nickel plated end caps are not that great.  I just did a comparison of cheap ceramic fuses between Bussman and Littlefuse.  In this case, the Littlefuse brand won out.  The Bussman had somewhat of a warmer/slower sonic signature.  The Littlefuse did not have this warm signature and was clearer/cleaner.  That being said, it was a stop-gap and I already have a couple of Hi-Fi Tuning Supreme fuses on order to replace these, lol.
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However, I don't necessary agree with teo_audio that you want silver-plated brass.  1 - silver plated can be useful, but in some situations it is just too fast/bright/harsh.  2 - Brass has never had good results whenever I have tested with it.  Brass usually pushed too hard on the signal and can come across as too strong/harsh.
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Furutech have wire/end-caps are pure copper that is Rhodium plated.  Hi-Fi Tuning Supreme is a silver/gold mix for the wire/end-caps.  Both are excellent, but have different results.

Honestly, I would rather get tin-plated beryllium copper (which is usually mostly copper with 2-5% bronze) then the most expensive silver-plated brass.  The tin plated copper is not that bad and it is definitely more neutral than silver plated or gold plated.