Do I need a Digital Audio Interface besides my Alesis Mixer

I have the full Producer version (64 bit), but the Essential would be plenty for what you want.

Here is the Sonar forums Cakewalk Forums

Check to see if you have "Sound Enhancements" option for your sound card. The enhancements include echo and reverb, which could be what you are hearing.

You need a PCIe sound card, PCI is dead. Better yet, you need an external recording device for best recording performance. Even a cheap recording interface unit will be better than ANY PC sound card (and it will take an instrument level or standard P.A. type microphone level input and thus better sounding voice overs.

Something such as this Alesis unit: Alesis iO2 Express Audio Interface | Musician's Friend

I have two MXL 990's (and another model MXL mic) that are "collecting dust". They tend to be too bright/trebly for most vocal situations. I've seen modifications to these mics on the gearslutz forum and one of mods even changes the actual condenser module to a different type.

The Shure SM58's are a workhorse on stage and for commercial applications. They are about $100 (on line at sites such as American Musical). Many local music stores will match prices with the on-line stores or the Guitar Center's (closest one from St Joe is in Independence).