Manley Jumbo Shrimp upgrade

It should probably be mentioned that for the fuse skeptic and/or audio cheapskate it's worth reversing the current stock fuse(s) in one’s system you know, to see if perhaps one way actually is better than the other. What are the odds? Gotta be 50%.

celtic66, you might check with Manley, providing your serial number, to see if there are any factory upgrades.

Otherwise, if you'd like to experiment I'd agree with trying a few different tubes.  I don't have experience with expensive fuses so cannot comment on those.

Of course one might ask what sort of improvements you hope to achieve before thinking about changing anything.

celtic66
I believe in your question you were requesting suggestions of who in the industry modifies the Manley Shrimp, or maybe both regarding technicians and types of mods. If you haven't already, I would contact Manley. I would think they would be able to refer you to repair and/or modification services/providers. Why not pose the question to the AG community of those owning the Manley Shrimp; what internal component modification they may have benefited from.
Also I found both repair and mod services for Manley products by an individual named Ben Jacoby. I have included the company address below.
http://www.highendaudiorepair.com/manley.html

Fuse directionality in AC circuits is technically irrelevant, and perceived changes in sound from reversing a fuse are likely imagined. Some think changing the direction meant you cleaned the fuse contacts and are hearing the results of that, but if the fuse worked before being reversed that's also very unlikely, although cleaning any contacts is generally a good idea. Like washing your hands after meeting a politician.

You  might, w_g, want to look at some other threads, where the person measured the fuse's output (I have no idea what thread it's on) and found that he could determine the correct direction.

And while your experience is unique to you, it's absurd to say that everyone else is imagining things. Some of us, who have been professional audio writers, know different. Why it didn't demonstrate an improvement is one of those things that seem to only happen to those who are dismissive of the experience of hundreds of other users. I can hear the difference in my PS Audio Power Plant between different brands of fuses, and can pinpoint exactly what is happening in the music - IF the recording used is not overly manipulated and is natural. Voices are the easiest way to demonstrate the improvements to me - as well as acquaintances who are not audiophiles. And it's not due to cleaning the fuse contact, that much I can say with certainty. 
I can't deny your experience, but my ability to hear is quite good, good enough for me to have written for a couple of magazines and been the editor for another one.  There are just as many people who are inclined to  toss 'snake oil' comments about a product as there are ones who believe the product's demonstrated - and  repeatable  - results. We're probably the same people who think AC outlets make a difference...