I'll try and clear it up a little bit
The Private Room (Inside the Silver Kris Lounge - First) - SQ First Class or SQ Suites Class Customers only
Silver Kris Lounge - First: All *A First Class passengers traveling out of Singapore in First Class, or Solitaire (Life) PPS members. Unsure whether if they are traveling on *A in Y class have access.
Silver Kris Lounge - Business: All *A Business Class passengers traveling out of Singapore in Business Class. PPS Club Members traveling in Economy Class on SQ are allowed, unsure if it's *A in Y what happens again.
* Gold Lounge - All *G Customers with a valid *A Boarding Pass