My question would be what OS are you using ?
The only reason I would suggest a-squared would be if you have an older OS (unlikely as you have MBAM installed) as there are better tools, SAS and MBAM being just two. If it is free resident anti-spyware (which a-squared has) then SpywareTerminator is better (IMHO).
Spyware Terminator Resident scanner (if you use this don't install the toolbar or crawler or the anti-virus module). This also would have no conflict with the passive spywareblaster.
However I would suggest paying the small one off charge and get either SAS Pro or MBAM paid option for resident anti-spyware/malware if it is the resident function you are after as both of these are better than ST or a-squared (IMHO).
ahh.. yah i know.. I'm still thinking whether getting the paid version of SAS.. I'm currently using the ff programs/apps/OS:
OS: Windows Vista Home Premium SP1 32-bit
AV: Avast! Home Edition 4.8.1296
AS: MBAM, SAS, SpywareBlaster, CWShredder, HiJackThis, Ad-Aware 2008 (not the AdAware AE w/ the "real time protection"), Windows Defender
Firewall: Comodo Firewall w/ D+ (without the AV module)
I'm just worried that Windows Defender isn't a strong "real-time protection" antispyware that's why I'm a bit bothered by it..