Full Range under $5k-ish

Here's a demo pair of Nola KO2s from a dealer who is apparently selling off inventory.  No offense to your Def Techs that are very good speakers for the money, the KO2s will bring you to another level entirely on every level.  The reason I'm recommending them is that they're overall awesome speakers, and the mids and highs are dipoles, which will image more like your speakers that I believe are bipolar.  These were $14k retail new, and you can get this demo pair for a little over $4k presumably with full factory warranty.  Buy these and thank me later.  If for some insane reason they don't absolutely blow you out of your chair you can probably sell them for a profit.  Maybe to me if I can get the wife to loosen the screws. 

https://www.upscaleaudio.com/collections/nola/products/nola-ko-loudspeaker

OP, as an x owner of first the P3 then upgraded to the P5, I felt there was better value to be had in their price range, but the P6 might be  whole new design upgrade. Dunno. May not be that big a deal spinning just vinyl

Parasound is pretty accessible to speak with whether the P6 uses the same phono as your P5

anyway, speakers. My room is ~1/3 bigger than yours and yet my Emerald Physics KCIIs are doing a bangup job with my kit. They're barely 4ft tall, slender semi pyramid shape, open baffle. I have 2 SVS Ultra subs which are turned off as I have ample bass without them. They are running  a special (or often do) for $1499. Run don't walk. Live happily everafter

PMC twenty/23 or twenty/24

Demo some of the larger Ushers and ATC SCM 40 and bigger if you can

OP, I appreciate the inconvenience of disconnecting your amps, but consider bringing just one amp and biwiring to get virtually the same performance.  A Carver TFM-35 is a powerful amplifier and doubt that the impedance characteristics of your speakers' high frequency drivers present any meaningful stress.  The TFMs have a distinctive sound (after all, TFM means Transfer Function Modified) and so it seems all the more important that you test the speaker/amp interaction.

My two cents.  Wishing you well!