Find efficient way of migration 2TB GBK table in SybaseIQ to UTF-8 files

My project need to migrate more than 2TB raw data from SybaseIQ to another Database. SybaseIQ using GBK, the target Database using UTF-8, the target database can only load from UTF-8 files. We use The Extract Options to extract data to GBK files first, then convert data into UTF-8, the converting is very slow because it's single processor only. Can anyone tell me the efficient way of extract data from SybaseIQ and convert charset and encode to UTF-8?