I was using a Topping pre90 with Benchmark AHB2 mono amps and LS50's (totally neutral). It was great. I just sold the Topping yesterday, which cost $600 new. I also used a Benchmark LA4 pre with the AHB2 and LS50. It sounded the same as the pre90. The LA4 is still better because it worked with all amps (plus more features) whereas the pre90 worked great with the AHB2 and Parasound A21+, a bunch of other amps had volume issues with the pre90. The Topping will be reviewed on Stereophile in Feb. So, it will not be a mystery component anymore.
I am putting my KRELL K-300i integrated on the LS50s now. Not because it is better than the per90 + AHB2 or LA4 + AHB2 combo, but because I did not want to sell the KRELL and needed a place to use it. It is a much warmer piece and also sounds good with the LS50, that extra bass from the KRELL is pretty nice.
I have Freya+ in my bedroom, and pairing it with the LS50 is not something that I tried nor do I think will be great considering my preference for the neutral sound of the pre90, LA4, and the AHB2 with the LS50. The KRELL is close to being too tubey for the LS50 but it does not cross that line.