Plinius SA250 MK IV upgrades? + SA Ref comparison?

I occasionally use this amp to drive PMC's MB2 monitors. Pre-amp and CDP are Bryston. In Class A, its smoothness, bass control, focused soundstage and colours/textures are great; it is 'musical' and easy to listen to. However, it doesn't have the top end extension and clarity of the leaner/'flatter' sounding Bryston 14B-SST2 which normally drives the speakers.

My questions are:

1. Are there any upgrades/tweaks which can materially enhance the SA250 MK IV's top end extension and clarity?

2. If not, has anyone directly compared the 250 MkIV to the twice as pricey SA Ref? I can't audition the SA Ref, so any thoughts are most welcome, thanks.
The rumour is that Plinius lowered the treble down a bit for the SA-102 and 250 MkIV versions because that's the way they interpreted customer demand. For the 103 and SA-Ref, it's back up. Again, just a rumour, read from a review.

Don't know of any factory upgrades but you can ask Plinius.

Try silver blend IC's/ speaker cables. Maybe Nordost. Maybe Ultimate Cables. Hard to go wrong on the latter, for the price.
There is possibly an aftermarket modification upgrade that is being offered here in New Zealand however this is still to be confirmed.
I asked Plinius years ago about the old SA VS the new SA series. I asked mainly because i sold my unit due to the background noise. Anyway, it's as Ngjockey says. Later series are more open otherwise it was pretty much same same.
I was fortunate enough to have my SA250MK4s modified in New Zealand where I reside which was researched by the man who was the main force behind the design of Plinius amplifiers prior to his departure in 2005. I was then able to make a side by side comparison with a SA REF which I had for 2 weeks. The modified SA250MK4 performed to a level beyond that of the SA REF. This was also confirmed by another Plinius SA250 owner who was present at the time. Mod is $900NZD and ensures long term reliability and improved sonics. Any queries email:
I also had the opportunity to make a side by side comparison with a Mark levinson 532h. Once again the modified SA250MK4 performed to a level beyond that of the Mark Levinson 532H.
No real surprise there, Samoanbowa. I owned a Plinius SB-301 that I found superior to the ML 532H as well - much faster and more dynamic.