EMS HK Speedpost is equal to the speedpost by Hong Kong Post Office. If you want to send a package with 4 kgs (actual weight) via speedpost, the charges is about 791. You can refer to the following website for details.
http://www.hongkongpost.com/doc/common/pos15a_rate_plan.pdf
If you sent it via air parcel through Post office, it cost about 425.
As you mentioned in above, DHL have quoted to you in $5,000.00, I believe the size of your package is very big. Otherwise, it would cause that much. If based on acutal weight 4 kgs, it should be around HK$2,000.00 only.