Subwoofer Suggestion

I just fear that maybe the sb1000 wouldn't go deep enough, and for the pb1000 not to go tight enough. 

Two of the sealed SVS-SB 1000 should do the trick!  

SVS or PSA over Focal or Klipsch. The 1000 series SVS subs are entry level and under-sized for that room. If the desired outcome is to add a little more bass, they'll do that, but if you're expecting a major improvement, you may be disappointed. Only one way to find out. Can you return them? 

Testing it wouldn't be possible. So since dual sb or pb1000 is underpowered would it be better if I go for a 15inch PSA S1500?

Can you return them?

It would be underpowered for me, maybe not for you. Forced to choose, I'd take two small subs over one big one for that sized room. 

I have quite a large room (28'x15x10-14', my ceiling slopes a little). I've rearranged this room a bunch of times and have had to find different places for my sub (REL T9). I only use it for listening to music (no TV). I've used the step by step set-up instructions from REL every time I've rearranged this room. I've been able to get amazing performance out of this sub every time. I think this speaks to the quality and thoughtfulness that they put into their products. There's one additional step I take setting up my REL. If you go down that road, DM me and I'll tell you about it.