Here's everything you need to know http://archimago.blogspot.com/2013/03/measurements-sony-playstation-1-scph.html
Here's the Stereophile review on it http://www.stereophile.com/cdplayers/708play/ note that the Stereophile review is on the SCPH-1001 model. Both models 5501 & 1001 share the same AKM DAC see the link above for more details.
I got mine modified with RCA output jacks and a couple of quality capacitors wired directly off the DAC chip
It pairs nicely with my Schiit Valhalla 2 and HiFiMAN HE-300 headphones, I'm using Audioquest Golden Gate interconnects and the stock headphone cable off the HIFIMAN HE-400 the one that's labeled made in Japan. The total cost of what you see here is well under $1000 bucks and Dude let me tell ya it sounds noteworthy. The musical factor is high like 420. The cost of this setup is well within reach for low budget heads and you could splurge on some NOS 6922 super duper tubes and still be under a grand total.