Which Floor standing speakers with the NAD C356 Int. Amplifier

generally one wants to get the best speakers possible and have an amp that can drive them w/o clipping (damping factor is usually not an issue these days, but if the speakers need a lot of current at some low impedance in the freq. range the amp must deliver)

beyond that you get into things like crossover distortion etc.

nad is well regarded ( I have a 2100 in my bedroom system) and yours is rated at 80W pc into both 8 and 4 ohms, so you need to look at each speaker for efficiency and your desired SPL, and then examine the impedance curve vs. freq.

once you have a few selected, hook them up and listen, recognizing that a new speaker will sound tight and restricted (if a voice coil design) until broken in

The budget is $3000.00.
So in your opinion, which speakers would have good synergy with the NAD given the size of the room.

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.

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.

I had the predecessor NAD C370 integrated amp / C540 cdp / C422 tuner driving different sets of quality-build floor and standmount speakers as a prior "B" system. I’ve also heard most of the recent models, so I know the NAD signature sound characteristics , strengths and warts, very well. This prior NAD gear speaker pairing included the TOTEM ARRO floorstanders; generally acknowledged as a nimble, forward, bright and transparent model in the TOTEM stable.

if you are looking for a a brighter and Improved audio presentation with a more enhanced upper midrange and top end, then move on from both:
(1) the NAD amp in favour of a quality built Euro integrated amp, and also
(2) an improved source instead of the OPPO,
instead of just new speakers.

(1) In brief, the NAD electronics present
(i) a comparatively "darker" overall and
(ii) a rolled off top end
audio signature.

(2) WRT the OPPO, I ran the top CAMBRIDGE Bluray player as a discrete stand-alone BluRay player for HT. (NOTE: The OPPO and CAMBRIDGE share the same motherboard made by the same company and also made in the same plant.) For HT multi-channel movies soundtracks and manufactured multi-channel audio, the CAMBRIDGE player did fine yeoman work in that role.....
BUT -- and it’s a big "BUT" --
it could not compete with my discrete stand-alone quality build high-end CDP/DAC for my 2-channel audio music performance requirements .... Not even close.

Your takeaway FWIW:

Going to different floor-standers with the same NAD integrated amp and the OPPO spinner won’t get to the Emerald City in OZ because of these inescapable NAD and OPPO sonic signature traits.

Nothing wrong with your gear, some of these guys are on a mission to replace any gear they deem inferior. 3 grand of new spkrs will make massive improvements.  check out these list for 3 grand. very sensitive

http://www.tektondesign.com/ddimpact.html

in 5 yrs you can post again about which cdp and amp to get right?

In a similar setting (nad352, 15inches from wall) I got great sound and massive bass from definitive technology bipolar towers--I used 8080ST, but the smaller 8060st might work better in a smaller room.