Basement bath drawin waste vent question

[Mlynch]

Installing a basement bathroom with toilet, lav and shower. The house main drain passes under the area where I'm installing the basement bath at a depth of 16" to 18" from the basement floor to the top of the drain pipe. Is it a bad idea to drain each fixture -- toilet, lav and shower -- individually into the main drain? Seems like it would be easiest to remove a six-foot section of the existing drain pipe and just piece together individual drain points.