Single REL T/9x vs S/510 in Small Room

My room is a bit bigger 19x15 w 10' ceilings..I run (3) S510..it sounds fantastic to me...I went from one T7i  to one S510  intially and it was eye opening...adding the second was a transformation...the 3rd behind was not so much and sometimes I don't even have it running..but IMO since the s510 has increased several hundred since my purchase last year I'd go with the T9x and bank the difference. 

Thanks for the post. 15 x 19 is quite large. Hence it is not a surprise that 3 subs work better than 1. Yes, the S510 costs considerably more than the T9x. Just unsure if there will be a noticeable difference if doing a one to one swap ie. from the PMC to REL T9x / S510.

Will decide and take the plunge when ready. The system sounds fine as is.

If cost versus result is a factor, use two T7x at least. 

There is a pretty significant difference between the two. The 510 is just “bigger” I’ve had both, kept the S510. The T9 does a pretty good job. I’m stuck with the reality of only having one sub floor space wise. My next move is either an S212 or another S510 stacked. As mentioned, two T9s would be excellent as well. But, if your option is just one do the 510.

I have a lot of REL including 6#25 and 2 510, and for a small room you need DSP, at the very least continuous phase adjustment

i would look for something more flexible than REL