Can you recommend a small (in size) Amplifier 150 -250 W Power per channel

Check out the Bryston B-135sst3 integrated.

It's not an integrated, but the Benchmark AHB2.  Without a doubt.  30 day trial.  You will not be disappointed.  Lowest S/N out there.  Small footprint.

https://benchmarkmedia.com/products/benchmark-ahb2-power-amplifier   

but in reality below 150-200 W does not go well

Usually when people say this, it means that the speakers require a very high current amplifier. If you are moving from the big FPB250m to a small chassis Class D amp, you are likely going to have to make some compromises in sound. I'm not saying it's going to sound bad, but none of these amps will have the current of the huge FPB250 with it's massive transformer, huge power supply and full Class A biasing. So, yes, you can probably find a small Class D that sounds good, but it is very likely not going to have the oomph and body of the FPB250.

Audio Alchemy DPA-1 (MSRP $1995) is  small both with both SE and XLR. Can be bought used ~ $900. That is a BARGAIN

Can you try Wired4sound. Class D amps.  I have one for a could of years. Very nice. 

Bryston 3b http://www.bryston.com/products/power_amps/3B-3.htmlEnd of search and unbeatable warranty.

To all of you above :

Thank you all for taking your time to help me with your suggestions. All of these are fantastic suggestions, each one appeared to be exactly what I am looking for. So now I have the daunting (but fun) task of choosing between these. And I really appreciate all your help.

Arun

gareneau91:

No I did not try. I jumped from Krell Integrated to Krc3+250s. Loved the change. Never changed my system since then.(Wish I changed the Wadias before the Company died, but they are so good).

A little off topic but arun3101, how did you find the match between the KRC-3 and the 250s? Did you try any other preamps with the monoblocs in your time with them?

Primare I35
Chord CPM 3350
Rega Osiris
Moon 700i
T+A PA 2500 R

Surprised no one yet suggested Gryphon Diablo 120 or 300 here. They are relatively smallish in size, and many describe the performance of diablo 300 to be surpassing many separates. 
I have this the 300 myself, highly recommend! 

Johan Darko has a series about Kallax-fi, small systems. Not sure if any amp was over 150W.

https://darko.audio/2019/02/introducing-kallax-fi/

Goldmund Telos 390 is the best for your speaker.

Love my Peachtree Nova 300, superb sound, gobs of power in a compact beautiful package.
https://www.themasterswitch.com/review-peachtree-audio-nova300

Second on Parasound great equipment for the $.

Parasound halo a23 great for the money

Forget the NAD D3020 for a pair of Mani-2 unless you want to throw 400 clams in the fryer and laugh as it cooks itself to death. Not even a contender for those Bruzzese beauties.

I had a pair years ago, having recently acquired a Wyred4Sound STI-500 those gems are back on my radar again. I would like to see how they would match up with this integrated. It is low profile in height but standard dimensions the rest of the way around (minus the hernia weight) with 250/550 wpc of power. Electricity sipping compared to the old Krell gear, as well as not being space heaters. Excellent grip on several speakers I have on hand. I never thought I would go from Krell to class D but I did and not the least bit bothered by it.

https://wyred4sound.com/products/integrated-amps/clearance/sti-v2-series

No mention of budget, but, Devialet class D are very compact and have a superb reputation for versatility, reliability and SQ.

Do you need small height or small width? (or both)?

What price range are you looking for?

The NAD digital integrateds are pretty good and very physically small. Look for the 3020D or I think 3060 D