Whilst there is no Diamond Lounge on Quantum, when numbers are sufficient they open up the Music Hall (Deck 4), for drinks and canapes from 4.30 to 8pm. This was the case on re positioning cruise last Oct from Beijing to Singapore and it was packed each night.
By the look of above posts, this is continuing for Singapore season.
Solarium on re positioning cruise and for the Singapore season is open to everyone over 16. On mainland Chinese cruises, Solarium is restricted to Suites and Diamond and above CA.