Adding a new disk to dynamic drive

I have a dynamic drive set up consisting of (3) TB SATA drives (all internal). My system (C-) drive is separate from this. My box (HP Pavilion Elite M9260F) won't accommodate any more disks space-wise, so I bought a twin SATA dock with the idea of adding two more TB drives. (what can I say, I like movies...) The SATA dock is connected to my computer by eSATA cable.
My problem is I can't (or don't know how to) add the new drive. It shows up under disk manager and I have formatted it when prompted, without assigning a drive letter. I thought I should be able to right click on my dynamic drive and click "expand" but that option is grayed out. Am I looking in the wrong place? Or is the option not available because an eSATA connected drive is not supported as part of a dynamic drive?
Here's a screen print of my disk manager
http://i46.tinypic.com/2i05cf7.jpg

There are two places you can right click the disk in diskmanagement -
1 where it says disk8 in yours - 2 the other vacant area to the right.
Read below I hope you find a solution - I highlighted a part in bold that might work.
The disk has no drive letter assigned hopefully you will be able to assign one after importing if that works.

Move Disks to Another Computer[This topic is pre-release documentation and is subject to change in future releases. Blank topics are included as placeholders.]

This section describes the steps to take and considerations associated with moving disks to another computer. You might want to print this procedure or write down the steps before attempting to move disks from one computer to another.
Backup Operator or Administrator is the minimum membership required to perform these steps.
Verify volume health
Use Disk Management to make sure the status of the volumes on the disks is Healthy. If the status is not Healthy, you should repair the volumes before you move the disks.
To verify the volume status, check the Status column in the Volume List view or under the volume size and file system information in the Graphical view.
Uninstall the disks
Uninstall the disks you want to move using Device Manager.
To uninstall disks
Open Device Manager in Computer Management.
In the device list, double-click Disk drives.
Right-click the disks you want to uninstall, and then click Uninstall.
In the Confirm Device Removal dialog box, click OK.
Remove dynamic disks
If the disks you want to move are dynamic disks, in Disk Management, right-click the disks that you want to move, and then click Remove Disk.
After having removed dynamic disks or if you are moving basic disks, you can now physically disconnect them. If the disks are external, you can now unplug them from the computer. If they are internal, turn off the computer, and then physically remove the disks.
Install disks in the new computer
If the disks are external, plug them into the computer. If the disks are internal, make sure the computer is turned off and then physically install the disks in that computer.
Start the computer that contains the disks you moved and follow the instructions on the Found New Hardware dialog box.
Detect new disks
On the new computer, open Disk Management. Click Action and then click Rescan Disks. Right-click any disk marked Foreign, click Import Foreign Disks, and then follow the instructions on your screen.
Additional considerations
When moved to another computer, basic volumes receive the next available drive letter on that computer. Dynamic volumes retain the drive letter they had on the previous computer. If a dynamic volume did not have a drive letter on the previous computer, it does not receive a drive letter when moved to another computer. If the drive letter is already used on the computer where they are moved, the volume receives the next available drive letter. If an administrator has used the mountvol /n or the diskpart automount commands to prevent new volumes from being added to the system, volumes moved from another computer are prevented from being mounted and from receiving a drive letter. To use the volume, you must manually mount the volume and assign it a drive letter using Disk Management or the DiskPart and mountvol commands.

If you are moving spanned, striped, mirrored, or RAID-5 volumes, it is highly recommended that you move all disks containing the volume together. Otherwise, the volumes on the disks cannot be brought online and will not be accessible except to delete them.

You can move multiple disks from different computers to a computer by installing the disks, opening Disk Management, right-clicking any of the new disks, and then clicking Import Foreign Disks. When importing multiple disks from different computers, always import all of the disks from one computer at a time. For example, if you want to move disks from two computers, import disks from the first computer and then import disks from the second computer.

Disk Management describes the condition of the volumes on the disks before they are imported. Review this information carefully. If there are any problems, this will tell you what will happen to each volume on these disks once the disks have been imported.

If you move a GUID partition table disk containing the Windows operating system to an x86-based or x64-based computer, you can access the data, but you cannot boot from that operating system.

Thanks for your response, whest. I figured it out. In reading your instructions I realized my new disks weren't marked as foreign, but it turns out the "Extend Volume" option when right-clicking the right-hand section of the existing spanned (dynamic) volume is only available (as in not grayed out) when there is a new disk with unallocated space available. My mistake was to format the disk which makes it unsuitable to be added. I deleted the volume and then it worked as advertised.
See the new screen print:
Image - TinyPic - Free Image Hosting, Photo Sharing & Video Hosting
I now have disks 8 and 9 added to the dynamic disk which now has 5TB available! Should keep me going for another 6 months...

Cheers, have a good time with that 5TB of space :).