I agree with Dgarretson regarding the Hovland caps.
A few years ago I swapped a pair of Tele 12Au7 tubes I no longer needed to Bob Hovland in exchange for a couple pairs of his Musicaps. My intention was to upgrade a pair of first order series crossovers which only used five passive parts; two of which were his caps.
I put several hundred hours on them but they always made my speakers sound too bright, lean and dry; "glassiness" would also apply.
Replacing the Hovlands with Mundorf Silver/Oil changed everything; huge improvements across the board!
Now, a couple years later, I'm still very fond of the Mundorf's and have used them in another series crossover with only three passive parts. My final tweak will be to replace the single Mundorf with a Dueland Cast. They're rediculously expensive but I'm expecting some very nice improvements.
Change the coupling caps in your Hovland and I'm guessing you'll probably want to keep it. Then again, Dgarretson and I both own Atma-Sphere MP-1's and might agree, if you really feel the need to upgrade, check out Atma-Sphere.