Best bang for buck integrated amp for $500

Rega is a great great choice IMO. 

You could get a used Brio-R in your price range.  They are truly excellent. No headphone jack tho. If you're patient you could get the newer model Used for $650-$700.  It will be well worth it - something that can remain in your system for a long time.

I've used my Brio-R to drive many different speakers - since it's small its easy to bring over to someone's house if you're demoing used speakers - it has never disappointed or failed to drive anything.  I've had Marantz, Rotel, NAD, Yamaha amps all in that price range and the Rega always sounded best.  It's super fun and always projects the rhythm and emotion of the music in a way the others don't.

I've loved my Brio-R for 3+ years and recently upgraded to the Elicit-R after trying several other $1.5k-$4k amps - again the Rega was the clear choice.   And still using the Brio-R for my kitchen speakers.

Also you'll be surprised how heavy it is, especially for it's size!

That’s super interesting @joey54 can you elaborate?

The nice thing about buying used is that you can try it and sell it if you don’t like it for little or no cost. 
Last time I went down this road I bought 4 amps (over about 6 months) and sold 3. 

Check out previous listing prices on hifi shark to determine fair market value. 

Can anyone detail some differences in the presentation between the IO and the Brio?

I’m guessing the Rega will bring a clarity, openness, and toe tapping rhythm to your setup. Let us know how you go!

I’d say first off - you’ll have to let the IO run in for at least a week. Let those transistors settle down after shipping and everything burn in. Listen to it for a week or 2 and then switch back and see what you think. I’d expect the bass to open up for you as well. Especially since you like the tone and clarity.