Compatible for iPad iPhone to HDMI Adapter Cable 6.35mm 1/4 inch TRS Stereo Jack Male to 2 Dual 3.5mm (Mini) 1/8" Stereo Female (Black03)

Q: Will this fir a polk sound bar (from my turntable)?

If your turntable has the 2 male (one red and one black) rca jacks to plug into these female adapters, and your soundbar has a female stereo1/4 inch input, it will work. Most stand alone turntables do have these rca jacks.

Q: Are the outputs really stereo? I purchased this and they are monaural.

They are stereo cables, of course, make sure you are hooking them up to a stereo device. I had no problem with them.

Q: I can use this to convert the audio signal from my turntables and have it go straight into my focusrite audio interface preamp?

This is an adapter, not a converter. It is designed to connect two devices together in one direction. Now, if you mean does it plug into RCA Audio cables (in stereo=right/left channels) out from your turn table then into the input of your focusrite audio interface preamp then it can do that. So, your turn table has to have a stereo rca out and then your focusrite audio interface preamp has to have a 1/4 (inch) female input. It is a stereo adapter, if you only have mono sound out, I would think it would still work to connect your two devices. However, depending on your wattage, the sound may not work the way you want. However, I don't know what your setup is exactly. If your turntable has female audio out then you need and rca cable with both ends being male. One end into your turntable and the other into the adapter.