Splitter on gpa 555!pre amp output

Each of the gfa 555 input impedance is 22kohm, using a splitter your preamp will see a 11kohm load.

If your preamp output impedance is 1kohm or lower it should be fine, otherwise the low frequency output will reduced. 

You have a GFP-555 preamp, two GFA-555 power amp, a GFS-3 speaker selector and two pair of speakers and want to connect all these thing up?

Please tell us how you want it to be setting up, play both pair of speakers at the same time? or you want to listen to one pair of speaker at a time?

By the way, if you want to play both pair of speakers at the same time, and bridging the amp as mono blocks and connect two speakers to each mono block is NOT advisable!

If you want to play all 4 speakers simultaneously, run both amps independently in stereo and remove the GFS-3 speaker selector is the best approach.

By the way, your GFP555 has two sets of output - Main and Bypass. It is safe to connect one GFA555 to Main input and the other one to Bypass input, OR you can connect both GFA555 to either input via a splitter.

Hope this helps.

Does anyone know if because I had two GFA 555s bridged it causes a need for a non common ground cable?

Yes, If you use the original interconnect cable to connect both Polk SDA 2B together while using two bridged GFA 555 to power the speakers, it may damage your amplifiers! That's why you need the SDA Non-Common Ground Amplifier Interface.

If you using only one GFA 555 in stereo to power both speakers, it is safe to use the original interconnect cable.