Phono Stage, How much do I need to spend, New or used.

You have $650 cartridge and $125 phono stage now.
I think you can fond some nice phono stages within $1200 and you don’t gave to pay more than this. 

One inexpensive phono stage I like a lot is JLTi mk4 which you could find for $700, now mk5 available directly from Australia.

You want to fill the room "like digital does"? Impossible. They all sound way better than digital. However, if you are asking what phono stage will be so good that even a guy like me who uses digital as the standard will be forced to admit yeah, this is WAY BETTER? Herron VTPH2A.

Or if using the MM cart then you have enough output to use the Decware ZP3.

I must warn you however, either one of these and your days of comparing to digital are done for.

That Mani really is your bottleneck. I have a friend with a Well Tempered Amadeus and Denon DL-103 who was using one. He replaced it with a Pro-Ject Phono Box RS (1000.00) and he says the difference was astounding. I would recommend my K&K Audio Maxxed Out phono stage (~2500.00) but I believe it is no longer in production. I have owned this one for over 20 years and it has been updated a few times. It's one piece that will probably outlive me.

So yes, a new phono stage will be a huge improvement over what you have.

Oz