/qb (basic ui) and /qn (no ui) are silent installations for MSI (meaning the UI sequence is not processed). There are special considerations for silent installs.
See:
Applying Patches
Applying Patches in Silent Mode
There are two ways you can apply a patch in silent mode: either launch
MsiExec.exe with the /qn command-line parameter, or pass /s to
Update.exe.
There is an important consideration to bear in mind when applying a
patch in silent mode. In order to operate correctly, the Windows
Installer property REINSTALL must be set to ALL and REINSTALLMODE to
omus whenever you apply a patch. Since Update.exe always sets these
properties at the command line, you do not have to do anything extra
if your patch package is applied with Update.exe.
When a patch package is applied with a full user interface, one of
your installation’s default dialogs, PatchWelcome, is displayed. It
includes control events to set REINSTALL and REINSTALLMODE with the
correct options. However, since this dialog is not displayed when the
end-user interface is suppressed, you must set the properties at the
command line, as demonstrated below:
msiexec /p 'path to .msp file' /qn REINSTALL=ALL REINSTALLMODE=omus
Because a patch does not modify the existing cached .msi database,
including the v setting for REINSTALLMODE is unnecessary.
FWIW, instead of using IExpress or writing your own extractor you could look at Windows Installer XML's Burn bootstrapper engine. It has an MspPackage Element that allows you to abstract all of this away and let Burn handle it for you.