First you did not tell us your musical preference, the sound you are looking for, what your system sounds like now and what you are trying to improve. I could recommend monitor size speakers or floor standers, but I do not have a clue to what you are looking to do with your system. IMO speakers should be selected first and then find an amp that mates the best with them.
Your rotel amp will mate well with Vandersteen spekaers and you can always find a pair of Vandy 3As for sale here, buy them and see if you like them and then resell for no real cost to you if you do not like the sound. They are slightly warm sounding but very musical. The are not rock and roll speakers but overall are a good value and a good starting point to see what you like and dislike about them. The B&Ws will also work well with the amp. Talon Audio Raven C spekaers are another good choice as they are very fast, have deep bass, extended highs, etc. They can be had for $3K used.
Some of the other speakers recommeded are good speakers but are harder to hear in your system and resell IMO.
Happy Listening
Your rotel amp will mate well with Vandersteen spekaers and you can always find a pair of Vandy 3As for sale here, buy them and see if you like them and then resell for no real cost to you if you do not like the sound. They are slightly warm sounding but very musical. The are not rock and roll speakers but overall are a good value and a good starting point to see what you like and dislike about them. The B&Ws will also work well with the amp. Talon Audio Raven C spekaers are another good choice as they are very fast, have deep bass, extended highs, etc. They can be had for $3K used.
Some of the other speakers recommeded are good speakers but are harder to hear in your system and resell IMO.
Happy Listening