Crisp sounding tubes for Modwright 5400ES

I recently upgraded from a Modwright 9100ES to a Modwright 5400ES. While there were improvements, the richer mid-range and more powerful bottom end of the 5400ES tipped my previously balanced sounding system into one sounding a bit overly polite with a lack if crispness in the top end.
Can anyone advise me on what tubes (output & rectifier) and power cables to chose so as to brighten the top-end.
Grateful for your advise.
I'm very sorry for "intervening" with this question, but I am curious since I have a stock Oppo 95:

Where does the stock 95 fall on the warm/full to open/detailed spectrum of the modded Oppo and Sony? Or maybe it's "outside" that spectrum?

Thank you

I'll let you know how the Synergy/Create 5AR4 tube sounds compared to Mullards when I receive it.
Hey guys, really appreciate all your help here. It looks like the first thing I should try is to swop out the Mullard 5AR4; then maybe try some other output tubes, maybe the GEs.
As for my cables, I'm using a Lessloss DFPC power cord for the 5400ES, and a Black Sand Silver Mk V for the power supply. From the power cable forums, it does not seem like these cables would cause my problem. As for ICs, I have tried Pure Note Vanguard and VH Audio fine silver DIY ICs. The latter helps to bring to lift the top end a touch.
In case any of you are interested, the rest of my system is Aesthetix Calypso pre-amp; Krell FPB300c power and Von Schweikert VR4jr speakers. I use a Hydra 8 power conditioner and a separate Hydra 2 for the Krell. I also take a lot of care in component a lot of care taken in system set-up with use of Herbie's accessories equipment & speaker support with accessories from Herbie's Lab.
Thanks again.

Wig, Yes, please do let us know. I will be interested to know if you also prefer the Synergy to the vintage Mullard in the ModWright. By the way, what year production Mullard do you have? Mine was 1969.