The budget is $3000.00.You have a nice amp and will drive literally dozens of floorstanders in your price range of 3K, either 8 or 4 ohms. It would be impossible for me to give you a meaningful recommendation of what would sound good to you.
So in your opinion, which speakers would have good synergy with the NAD given the size of the room.
But you have several advantages - you're not crazy about how your current MA Silver S2's sound and you have a decent sized room to keep rear ported speakers 15" from the rear wall. Also, be aware that your MA's use metal domed tweeters so maybe its time to start auditioning brands that use soft domes instead. You may find their sound more to your liking in addition to the deeper low end frequency response a floorstander will give you with its greater internal cabinet volume.
So do you have anywhere that you can start auditioning? If so, bring music you are very familiar with and pay attention to driver construction, complement, impedance and sensitivity. Don't concern yourself with price at this point as your trying to discover what sounds good to you. And not us. Good luck and have fun.