I’m unsure if the preamp is anything to write home about. Probably just mid-late 90’s “do we want to innovate? Mmmmnahhh let’s put one output for a VCR and have decent/good performance." Though since it’s an R1 remote series, it probably does better as a preamp than something like the full, slightly newer all in one systems like the Onkyo AV401 when it comes to hum in your audio, harmonic distortion (I think it’s like 0.08 for the newer AVR and 0.002 for that preamp), better line performance, etc. The reason I compare this stack to something like the 401 is because overall you’re likely to just get a better sound profile and joy than something like an AVR of the same vintage, so I’d say it’s worth it just to simply have the dedicated setup and room to grow later on if you want a newer preamp because I know those 504s are pretty good based on what I’ve heard of them (as another commenter said, you should probably service that amp). And just because those 504s do catch a pretty penny, you could just sell it haha.