ok...
Let me recap.
1. You have the HKS SSQV and your bro has the Type RS.
2. You swap to the RS and try to install some aftermarket FMIC.
3. You give up, and put it all back together as it was, stock IC, etc...
4. You only get 4psi now.
5. You put the HKS BOV back on in case the Type RS was leaking.
Is this correct?
With no boost controller, you should see at least 8 psi with the mods you have.
Do you have a 3" turbo elbow?
Did you disconnect your MBC when attempting the IC install? If so, please check and make sure that the MBC is not hooked up backwards.
Did you possibly damage your IC when removing it?
I would move the vaccum line for your boost guage from the intake manifold to the front of the turbo. This way your boost guage will show what your turbo is doing. If the turbo is blowing 10, and your intake is seeing 4, then you have a MASSIVE boost leak.
If the turbo is only blowing 4 psi. Then check for an exhaust restriction.
Do you have a check engine light?