So what you did was take a line out from the Onkyo and run it into your amp. The line out probably says Tape Out and is intended for tape recording. As such it is line level, ie about 1-3 volts in level and fixed. So in other words you are using the Onkyo as a phono stage and nothing more. Which is fine. Because now you have that Onkyo phono stage as a baseline.
If its not clear don't worry that's normal. Most people just hook stuff up, never do understand what's going on.
This is how it works. You hook up, you listen, you compare. Or you run around throwing money, which is what most guys do. Listen and compare takes longer but you actually learn a lot more and go a lot further in the long run.
Like, already you have heard and learned what the phono stage inside your Onkyo sounds like. The pure phono stage, without even a volume control on it. That's not nothing. That's your first baseline component. You have just auditioned your first phono stage.
Now for $6 plus shipping you can get one of these
https://www.parts-express.com/boss-b65n-speaker-level-to-line-level-output-converter--265-4040Connect the wires to the Onkyo speaker terminals, connect the RCA to your amp, and now you can use the Onkyo as a pre-amp. Yes you can do a lot better- but not for $6!
Doing this will remove the urgency to "do something" and you will also now have another baseline from which to compare: pre-amp. So now if you want you can bring home a pre-amp to audition, or another power amp, or even an integrated and use the Onkyo phono-stage, see?
Because ultimately what you are probably going to want is a new amp, pre-amp, and phono stage. But remember we're talking functionally. You do not necessarily need those three components. You may find an integrated with built-in phono stage that sounds fantastic. Or you may find an integrated with a separate stand-alone phono stage that sounds even better for the same combined price. Or who knows, you might even find a pre-amp with phono stage that together with your existing amp sounds great. I think that is rather unlikely. Everything multi-channel for HT is almost always pure crap, sound quality-wise. But you never know. Everything works together. Could be the money you save using the amp lets you buy a much better phono stage that sounds so much better it makes up for the HT amp.
See what's going on here? The only way this works is by trying this stuff out and actually listening to it. I could never adequately explain how well this works, but I think it will become clear if you actually do it enough.
Something else to keep in mind while you're doing this- everything works together. Everything. Everything includes speaker cables, interconnects, power cords. Pay attention when you go into stores what they are using to connect everything. Don't just listen to a component, have them change and let you listen to different interconnects and speaker cables too. Done right, taking time to try out and compare all these options, takes longer but you will be shocked how much difference it makes in the end.
