Crisp sounding tubes for Modwright 5400ES

Thanks to all of you for your advise. One thing I neglected to say was that I had already switched to using a Mullard 5AR4 and Sylvania 6sn7 GTBs; sorry for that.
I had read elsewhere in Audiogon forums that the Mullard can be a bit 'overly-sweet' sounding, which I take to be overly-rich? So I was looking initially to change the rectifier tube for something which would give a crisper top-end. I read in another forum that the EML 5U4G has a more more open top end. Has anyone tried this?
Jwn, thanks for the benefit of your experience with the Oppo. I did think about this but then stopped when I read the following thread, where their observation was the the Oppo was fuller and warmer sounding. I am sure your experience was valid in your system; I guess that's the thing with our hobby; there are so many combinations and permutations and different outcomes in audio.

http://forum.audiogon.com/cgi-bin/fr.pl?ddgtl&1324431696&openfrom&1&4#1

Many thanks Wig for this; it sounds like the Create 5AR4 is just the ticket for me, as what I want is to trade some mid-range richness for some more crispness at the top end. Can I ask where did you got this tube? I also agree with you that swopping the rectifier tube can make more difference than the output tubes. It definitely was the case in my rig when the Mullard went in!
Thanks also to Brownsfan & the other guys for the benefit of your insights. I swopped out my Mullard for my stock rectifer tube, a Ruby 5AR4, which helped to restore some of the top/mid balance to my system. Can't wait to try the Create!

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.

Thought you might be interested to know that after I swopped out my Mullard 5AR4 for the stock Ruby rectifier which my Modwright was supplied with, the frequency balance in my system returned. I then bought a Create 5AR4 (living in Hong Kong, I got it direct from China). From new, I was a bit surprised to hear hardly any difference between the Ruby and the Create. If anything, the Create was a little softer and the Ruby a bit more dynamic. But upon swopping the two to compare, I noticed they look very similar. Further examination confirms it, the base was identical, in colour, material and moulding. And the parts inside the tube also are effectively identical, apart from minor differences due probably to the fact that they are hand assembled? I probably should clarify that I am not saying that Ruby and Create are identical tubes. All I am saying is the two look very similar to each other. Maybe the factory that makes Ruby 5AR4s makes tubes for Create too? I will put some hours on the Create and do another comparison with the Ruby and keep you posted.