There is always will be a latency while you trying monitor your line-in input in real time.
But Phoebus has much more bigger latency in Windows 7,compare to Creative Audigy 4 and EMU products.
I have the same problem with this card.
And there is no workaround,unless Asus will fix their driver,but I`m doubt about that.
Still you may try to use any software DAW in ASIO mode.
But there also many bugs.
Do not use Presonus Studio One,cause Pheobus don`t work with it at all.And it is VERY dissapointing.