Adding a sub woofer?


Running a Planar 6 to Icon Audio Ps1 Mk2 to Quicksilver Mid Monos into Klipsch RP8000F speakers. Want more low end, thinking of adding a sub. The mono blocks don't have a dedicated sub output so I was thinking about something like a PSB 250 which has both pre amp and speaker level inputs with speaker level outputs. A couple of questions.

What are the pros and cons of using the sub's preamp level inputs vs the speaker level inputs in this application?

And more importantly, right now my setup is pretty much tube analogue the whole way (and aside from the soft low end, I absolutely love the overall sound) - but does an inline sub like this do any processing, will it color the mids and highs in some way or is it just a clean pass-through in terms of sending the signal along to the speakers? 

Thanks for sharing your thoughts. 
Ryan
spotconlon
I prefer using line level with any sub that I have owned. Some prefer speaker level. It all depends on the main speakers that you are using with the sub.
REL has been around for 30 years so I would not call it a current fad!
https://rel.net/our-story/
I believe REL were the initials of Richard E Lord the products original designer.
Speaker level or line level is all the same and has nothing to do with the speakers used. Here's a very good technical article that explains exactly what the difference is: two resistors. https://www.epanorama.net/circuits/speaker_to_line.html/ This actually works, by the way. Its what I used to add a pre-out to my tube amp, as per the mod shown in the last photo. https://systems.audiogon.com/systems/8367


Pick your so called expert carefully, there is a massive difference between line and speaker level as the latter passes the sonic signature aka transfer function to both the sub and main speakers which results in better more coherent sound. Those with a poor understanding of bass fundamentals AND harmonic content will not get it. Bass, coherent bass is alive well above 100 hz.
for a phd in active bass with high pass mains research Vandersteen subs.