Ok, I'm not very familiar with Seri's UI so let me know what you think of this suggestion and whether I'm on the right lines.
I'm guessing that changing your existing HP / End bar in the centre would be a pain, that looks to me like it's part of hotkey 1, so resizing that means re-working all that code. However your actual player window appears to be the transparent bars just to the left of centre in your main window (I can just make out a tiny combat timer).
That being the case, they're already free floating so adapting those to enlarge the bars and add the text in a larger font should be a piece of cake.
What bars do you want there? Do you want to keep the target and hott health there too? And how is this for a layout?
[ \ / ] 1111 [-------------------- ] 2222
[ / \ ] 3333 [-------------------- ] 4444
So you've got a large combat graphic on the left (I'll fit the timer in there somewhere too), and on the right you've got your current health/mana on the left of the guages and your max health/mana on the right.
If that sounds ok let me know and I'll have a go at it this week.
Myx
PS. Very interesting to see a UI at 1920x1200. I can see me tweaking my UI to come up with some better settings for that resolution