SBX prostudio is one of, if not the best virtual surround sound algorithms available; but, audio preference varies so much from person to person, so it's not so simple to say that it will work for everyone. Dolby Headphone, for example; not as good as SBX prostudio, but there are people who find it really good; others, think it sucks.
The only option that is as good as, or better then SBX prostudio, depending on opinion, would be a Sennheiser GSX1000. Whether it's better or not will change depending on who you ask. Some people who own a GSX1000 find it a lot better than anything else; but have I seen a few people say they returned theirs because they thought Creative's SBX prostudio was better.
GSX1000 is not cheap for what it is though. AE-5 and G6 have better hardware and they are cheaper. GSX1000 would really only be worth a punt if it can be bought significantly cheaper than the £200 RRP. Even if you were to consider getting one, it won't drive those K612 headphones well enough. Output is rather weedy compared to the Creative's, more geared towards driving Sennheiser's gaming headsets, meaning you'd need to look at spending more money on different headphones.