Naim gear is a bit laid back. Good sounding and quite detailed. I find it needs to be paired with a very energetic/forward speaker like Focal which is its sister company. I was listening to a Naim xs2 with some Spendor speakers and it was very laid back.

Rega is warm but pairs well with speakers that are slightly forward like Revel. The Elicit R is a wonderful integrated. Very musical and I am a huge fan.

It has been a long time since I listened to a Roksan and remember it being less warm than Rega but not quite neutral. I believe it was the K2. Nice amp with oodles of power but not the be all end all in clarity and refinement.

I have never heard the unison research and have no POV.

My vote would be for the Unison Unico Primo. Lovely gear & well made. But if you're open to used gear, there are some nice, musical sounding integrateds under $3k. I found this Hegel H300 on US Audio Mart in good shape, asking $2.6k - https://www.usaudiomart.com/details/649463087-hegel-h300-integrated-amplifier/ The Hegal also has a decent dac, so you can connect a laptop or mac mini.