Hi
@teej,
Honestly, specs aside, all depends on you whether you want dual sub set up or single use of either sub & switch between them.
What is your main usage for the sub or subs ?
It is all well & good to hear about a dual sub or more experience but have you experienced this yourself at demos &/or audio shows to see whether you even like it in the first place?
For example, for my own system, I normally run a 2.1 - 4.3 where the .2 is built in to one speaker pair I have.
I also have another speaker pair with built in subs I could use in tandem with above & have or by themselves.
Given current set up & overall placement, it is not necessary for me to run a 6.5 but I could.
For me just the 4.3 is more than enough though saying that, I wouldn't mind another dedicated sub, budget permitting but personally, there is no rush or real necessity.
Now where specs are concerned, there are a number of things you can do regarding setup.
First of all, I would be curious to know your current settings from the PSW 10 then go from there or just leave them as they are & follow what I suggest below for the Elac sub.
Either way works as long as you find the right balance if using dual.
Also, do you have a spare RCA out on your Sony AVR for the Elac Sub or will you have to get a splitter to share the signal on the same output if you want to try both simultaneously?
Since the Elac sub is technically more powerful watts wise, I suggest not putting the volume knob past 12 o'clock & the phase knob anywhere between 80 to 90 as this generally gives the best balance of quality bass from low to mid volume & any media which goes down to the 5 hz level will be picked up easily once it reaches the Elac sub's minimum range though tuning wise, it may pick up the lower frequency sooner.
This will also not potentially 'overpower' the PSW 10.
Concerning placement, it all depends what you're trying to achieve with either sub &/or both, are you going for eg, room fill, general bass response, quality vs quanity, etc
Corners & walls all have their pros & cons so what may be considered 'wrong' to somebody may actually be good for you, relative to your own experience.
Unless distortion &/or clipping, 'muddy' or 'excessive bloom', reflections are obvious but once again then you don't want these.
Acoustic panels & the like do help address some of the more obivious issues but are in no way indicative of making things 'better' but they can help.
So the best advice I can give here, is experiment & see what works for you.
Subs especially don't necessarily have to be against a wall or coner for reasons I mentioned you don't want & can sound great away from these particular spots.
Hope this all makes sense, feel free to ask me more.
Hope you have a great day !