Hi Timothyd11
I have experiences with the Niles AXP-1 as well as the Niles DSP-1 and IME I have never experienced any sound degradation or coloration at all.
I used the Niles AXP-1 when I had a preamp with limited inputs but I had multiple sources.
I use the Niles DSP-1 to use 2 different kinds of amps with the same pair of speakers. My only issue with the Niles DSP-1 was the speaker wire connectors in the back. It states you can use 14 AWG but it the spacing did seem kind of tight.
I'm not sure but with your situation I would get the Niles AXP-1. Both are built quite well and are solid quality.