6k is slightly below market rate...Almost 60% of my friends are getting married these 2 years and the rate is about 8k - 12k. I am quite lucky because my hubby suggested to give 10K due to both his brother in laws gave 10K to his parents 6-7 years ago when his sisters got married. Hence, my hubby & in law knew the market rate.
Besides refunds part of the money (woei lai) to my hubby, my parents used the money to buy gold/diamond to me & my husband which cost around 8k and this was actually 2 years ago. Gold/diamond price now are much more expensive than 2 years ago. Therefore, your parents are very reasonable & understanding already.