Older vs. newer REL subs


Looking for any reports about older vs. newer REL subs.

I have a REL 328 (ca. 2013) which I bought used. It's a good sub.

https://www.hifiplus.com/articles/rel-r-328-subwoofer/

I would like to upgrade to stereo subs and I've found (finally) another REL 328 which would match mine. But, before I drop coin on that, I'm wondering if anyone has had experience comparing their older REL with a newer one. What's changed? What's better, worse, or the same? I'm considering the T7x and T9x lines.

Hoping for apples to apples comparisons, vis a vis driver size, type of sub (e.g. level of product line, sealed vs. ported, music vs. HT etc.) but whatever old vs. newer comparison you have much appreciated. 

Thanks.
128x128hilde45

@shahram I got two Rythmik subs. In addition to the REL, I was able to position and adjust them to within +/- 4db between 20 and 400 Hz. Sounds excellent. The Rythmiks' adjustable phase was what made it all possible.