If the shower drain is below the level of the main drain, you need to use a sewage ejector/sewege pump system. If it's for waste, yes a grinder is needed.

Sewage Pump System (Barnes)

It requires digging a pit and running lines in the concrete.

Ejector pumps are only worth the hassle when your sewer main comes in the house higher than your drain. A typical scenario would be installing a basement bathroom where there wasn't meant to be one. They break down occasionally and require maintenance.

Busting up the concrete isn't as hard as it might seem-- you should just do it the right way.

Get a masonry blade for your circular saw, cut nice clean lines where you're going to be removing the concrete, then rent a jackhammer from the box store. It will take maybe an hour to get through that amount of concrete.

Do your plumbing as usual. Put your dirt back in. You'll have space leftover. Use sand to fill it (don't use the old concrete-- sharp edges will cause problems). Mist it with water and and tamp it down between bags to ensure maximum compaction.

Mix concrete in a mixing tub from the box store. Do yourself a favor and don't buy the rapid-set kind. It will give you time to work. You can mix by hand with a cheap garden trowel. Pour the concrete, run a 2x4 over it to smooth it out, let it sit a bit for the water to rise, then use a trowel to flatten it out more. Voila.

Lots of videos on YouTube to walk you through it if you want to take a stab at it.