Using Rom Manager was a mistake, but probably wouldn't brick your phone. It just doesn't play nice with the S2, tends to cause bootloops & break recovery.
If the phone won't boot at all, no download mode, no recovery - your only option is service centre or local mobile repair shop. Nothing you can do to fix it.
I mean, try a jig by all means, but understand this is very unlikely to get you into download mode.
Having said that, you need to be 100% sure you can't get into download mode (power/home/vol down), if it was me in your situation, I'd be trying over & over & over given the alternative.
If it's important enough to cause you grief if it's lost, back it up. No excuses
Trolling for thanks is lame
Does Samsung's auto-brightness implementation crap drive you to self-harm ? A solution !
Probably the best thread ever posted on XDA
Failure to search is the leading cause of male impotence on XDA
If you don't know how to recover if things go wrong, what are you doing flashing custom roms ?