need to upgrade my center speaker

i have Harman Kardon 30s front l/r and rears 10s. w/thier center. Its ok but would like to upgrade. how would i match to my other speakers. i am 75/ht to 25 music at best. thanks.
Don't know what the impedance of your speakers are or what
you are using to run them, but the Energy AC300 which came
out several years ago is a GREAT-SOUNDING speaker. I'm
using it as a center with Thiel 1.5 L/R with Analysis Plus
Oval 12 cables. The clarity and soundstage is fantastic!
It does have a 6 ohm impedance. Used to be an Editor's Choice on

Good luck.

Try KEF Reference 100.

Its neutral, not bright like Thiel, 6 ohm impedance, bi wire. Supurb for voice, and a big % of HT is dialogue.
Spendor SC3, also. I have a front trio consisting of the SP3/1p and the SC#, and the sensitivity and flawless coherence of this grouping was PERFECT straight from the get-go. Extraordinarily natural!