Help in hooking up a sub woofer.

As I see it you cannot use the subs with only RCA connection. In your case the only way to integrate a sub is thru the speaker terminals. A different kind of sub is needed.

246810:
" I would want to keep a direct connection to my current speakers and run another direct connection from my amp to the sub. Is that an electrical reasonable method?

Hello 246810,
    What gillatgh stated is correct, your only choice is to get a sub that can be connected thru the speaker terminals.
    Your preferred method of connection, quoted above, is exactly the connection method you would use for either SVS sub. Yes, it is an electrically reasonable and safe method of connection. You'd just need to ensure your PrimaLuna and sub are not powered 'ON' when making the connections.
    Once all connections are made and you turn on your amp and sub, the final steps are to precisely adjust the Volume level, Crossover frequency and Phase setting until the newly added bass output of the sub seamlessly blends with the output of your PSB Synchrony1Bs.  
     Ideally, you would use a CD with test tones playable at your crossover frequency (I believe it will be between 40 and 50 Hz) to properly set the volume and phase settings on your new sub.  Do you have a cd player?


Tim
  

Hello Tim,Thank you very much for that information. Getting that Sub with only RCA jacks actually surprised me. I would have never thought it would come like that.To answer one of your original questions which I failed to do; I use my stereo for music only. I'm not much of a TV guy and certainly not a home theater guy, I own 3 dvd's; The Last Waltz, Roy Orbison Black&White and Dr Strangelove, ha.
I have my old "5 Disc" Yamaha CD player, which I kept because it has room for 5 discs for background music during the day. About a year ago I finally made the deep dive in to the digital world and bought a Marantz ND8006. It's a combo CD player and streamer. My first attempt at "streaming". I like the CD player; it's decent enough for me. I also have my faithful old turntable (well it's not that old) but I bought my first record player in 1957 and have had one ever since.My faithful little PSB's still sound pretty good to me and I listen to every thing but opera.
I may be able to incorporate a sub into this system at some point, I am just really jammed for space (hence the "toy")Thanks for responding, and actually telling me what the connection should be, I appreciate it. I really wasn't getting that anywhere else.

Hello 246810,

     Well, it seems like you're not going to buy a decent sub anytime soon due to your lack of space.  Maybe I'll respond to a future thread you post when you're ready to add a sub or two.

Good Luck,
Tim
  

@246810
What you need is a speaker level to line level output converter:

https://www.crutchfield.com/S-DtVn9IwgHWx/p_543ADP12/Russound-ADP-1-2-Speaker-level-to-Line-level-Ad...

It is just a simple voltage divider, contain two resistor in each channel.