Can't decide on Integrated Amp - Please Help

Hi, really trying to find the best deal I can on a used integrated amp. My current set up is

Monitor Audio RX6 speakers
Oppo 105

Looking for a strong integrated that if I wish to upgrade my speakers will easily handle the change.

Looking at spending no more than $3,000 for a used example and would love some help. I stream most of my music through the Oppo instead of CD's and listen to a lot of Pink Floyd, Dave Matthews, Sting etc

Few choices i have outlined and really hard to be able to audition anything and would like it to match the speakers and Oppo well

Rega Elicit - R
Krell S550i
Hegel 200 or 300 if can afford (is the DAC much better than the 105)
Stello ai500
Saw a PLINIUS HAUTONGA Intergrated A but don't know too much about company.
Modwright 200

My room is around 15 x 15 with wood floors

Thanks in advance for help
Thanks for all the advice so far.Donjr did you try the Rega Elict R as I have been given an awesome price on a used model. Also in relation to Hegel I agree the unit is ugly but I hear nothing but good reports. They are bringing out Hegel 160 soon to replace 100 and 200 so may wait. Did you happen to compare hegel 100 with 200 - is there much difference?
Simonmorty-I heard the Rega Elict/Apollo driving a VA Haydn and was not impressed. IMO a $1500(new)NAD 375BEE is a better amp. If your looking for a used amp under $2K consider a Marantz-S11/2 which is competitive or better then all amps on your list, and should be a good match with Monitor Audio.
Hegel would be my choice. I also have a sim audio 5.3se I am not using if you want to buy that.
I'll second RW on the HK 990. High quality, lots of power, and unmatched flexibility (particularly the bass management and DSP). If you're looking to future proof yourself, I don't think anything else out there can match it. NAD also makes a unit that barks up the same tree, but I prefer the HK.
Hi Martykl. So how does this unit you recommend compare to say Marantz units i.e AV7005, AV8801? I have previously owned the Marantz with a Rotel RMB1075 and the sound was good. However looking for a more superior sound and would find it hard to believe although good that the HK990 could compete for 2 channel audio with Hegel 200 or CJ CA200? Maybe I'm missing something and open to suggestions. Thanks