There's a whole process to it. It begins with getting a high quality signal in to the machine. That includes using great mic pre's and mics. Then comes the mixing, knowing how to eq. There is compression involved, there is limiting involved. Once it's all mixed then comes the mastering.

While mastering engineers can pump up the volume, they can only do so much. It's really a combination of things to get that result. It's generally not secret gear, but them really knowing how to use the gear they have.

In answer to your specific question about your demos. There's the key word in your question, 'demo'. The studios you're working at may not have the know-how to get those levels. They might not have the great mic pre's. They might not have great A/D converters. As to why "joe-blow" studios can't figure it out, they may not be willing to learn. It's not as hard as one might think. Or they might not have the ears. And ears are something you have or develop.

Jody

p.s. - great mastering does not have to cost thousands.

Jody Whitesides
A Funky Audio Lap Dance For Your Ears!
www.jodywhitesides.com