I just have enough USB to serial converter which will fail occasionally.
So , I decided to put aside some money to buy a PCI-e to RS232.

Bought this board from All-IT digital mall.
desktop-pci-serial

Once installed , the windows machine detected it accordingly.

serial

which represented as COM5 and COM6.

Now to add this to VirtualBox, In setting just need to specify the host device as COM5 and mapped to virtual O/S serial.

host-device

and inside the box, we would be able to access as normal port. /dev/ttyS0 on CentOS 6.

minicom-ttyS0

yay!