James Larson,
Since you have measured and reviewed both, do you think the Monolith THX-365C center would be a decent tonal match to the Polk R700 as left and right channels?
Measurements for both look pretty flat and neutral, so I'm thinking the tonal match should be good enough to not be distracting. Erin's Audio Corner also recently posted Klippel analysis on the THX-365C, confirming the very good measurements for this center.
I just received a pair of R700 and have been using the Monolith THX-365C for about 2 years now. The R700's will replace a pair of 30 year old Polk LS90 floorstanders in our multichannel system.
BTW, been testing the R700 with 2 channel music in another part of the house and I think they sound really, really good. Also, they have excellent packaging and arrived in flawless condition, other than 1 loose screw on one of the bottom plates. They seem to be constructed very well (heavy for their size), and it seems like Polk went for no-nonsense performance on these speakers, putting the budget and design effort into performance, rather than exotic materials and a fancy cabinet finish.
As a side comment, I really wanted to use a pair of Monolith THX-460T floorstanders for left and right, but I bought a pair in April '21 (and even exchanged 1 of them), and all 3 had multiple scratches that looked to be from mishandling at the factory. I could never get an answer from Monoprice on whether the factory handling issue had been resolved, because I really wanted to try a pair again. I gave up and moved on, ordering the Polk R700 when they were on sale last week.