Need to learn about Audio Research

I still have a LS25 mk1 made in 1998 from what I see , it's still rocking 😎 

Got all new capacitors about 4 years ago, and voltage regulators . Great preamp!

Agree that tube pre + SS amp is a good “warm” direction to go from the Hegel H390.

A GanFet amp, which is similar to a warm sounding SS, may be a good option.

Krell K-300i integrated has “150Wpc into 8 ohms and 300Wpc into 4 ohms, with its iBias technology allowing the amp to deliver up to the first 90W in class-A (warmth) —"without the excessive heat and power consumption of traditional Class-A designs,- (Stereophile)

I have used ARC AMPVT150 mono with LS5 preamp since1996, sweet amps to replace McIntosh tube amp/preamp. , there was no mechanical or electrical failure.

My current amps are 160M,without repair last 4 years.

AR is coming out with  some NEW AMPs/preamps SS/Tubes in 10 K range starting in April 2025.

I have decided SS will be the way to go.

Good decision. There are many maggie owners who have had a tube amp on the tweet/mids and a solid state on the bass panels but you don’t have that biamping option with the 3.7’s, not without much more extensive modification at least.

A friend is going to loan me a parasound A21 soon.

That should work out, let us know how that compares to the Hegel.

What would the pre be with it though? 

You should keep the H390 and add a Tube Preamp and/or even a Tube DAC like Primaluna. You’re not going to get better for less than $10K than the Hegel.