Sansui AU-D9 at 4 ohms?

Your next stop should be minimum of 2x the current power, plus::
So, 100 a side? I'd double down again and go for 200 a side. Anything less will not be enough, IMO.
The 95 watts of the Sansui won't be enough, I guarantee it. You'll want to trade up again in 6 months.

2 things going on here. Steady level and Peaks. By going to the Sansui you will add power for peaks. You will be able to turn it up just a little.....than be back where you are now.

I'd save for another couple months and see if I could go up the food chain a bit.
Your new Magnepans will put more strain on an amp but are really not a 'bad' load. You might not have noticed, but your Nikko is running warmer than it did before the panels.....or did it come with the panels?

A good, NEWER, more powerful amp can be found in the likes of NAD and some others.

Sansui has made some good amps like the AU 919 or the AU-X1 but these amps are now around 30 years old. I would also suggest you look for a newer amp. Music Direct now has a Marantz integrated that lists for $1000 on sale for $600, or NAD as Magfan suggested.

I may be pushing my luck here,
I usually don't like the 'get this' kind of answer.
But in new amps, Onkyo makes (made?) the A-9555 a 'd' integrated which got some pretty descent press.

http://stereophile.com/integratedamps/907onk/

Test is just now 2 years old.

At the stereophile measured 175watts into 4 ohms, you get a very usable near-6db boost over your current Nikko as well as what would appear to be at least a usable phono preamp and some questionable tone controls.

Maybe still new? preowned with a couple hundred hours? such a deal.