CGK Transit
With the new information, I can confirm what the last posters have said:
1.There are no arrival lounges at CGK T2 but WITH a through Boarding card you CAN transit to another International flight by taking the escalator on the right before going down the slope to Immigration. So if you can do an online checkin in Singapore you will save the USD10 Visa fee (For one week) and the IDR 150K Airport tax for International flights. This assumes that you have no checked bags because if you do the bags would NOT go through, nor would SQ check them through as they have no interline arrangements with Air Asia.
2.WIth a *A Gold Card (Or even PPS for that matter under the present rules) you would NOT be given access to the SQ departure lounge on an Air Asia Boarding card. There are 3 lounges in T2 departures, all down the end near the A Gates and you can, however, pay to enter. I understand it costs about IDR150K but not sure because I have never had to do so.