Check the listing for details. Comrex STAC Hybrid Studio Phone System Rack Mountable w/ STAC Control. Condition: Used. Listed at 950.00 USD. For sale is a lightly used Comrex STAC mainframe and controller. It was taken out of a studio working, but I have no phone lines and I am unable to test. The Comrex STAC Classic is a hybrid studio phone system designed for professional audio applications. With its rack-mountable design and STAC control feature, it offers a versatile and reliable solution for podcasting, broadcasting, or any other audio recording needs. The Comrex brand is known for its high-quality audio equipment, making the STAC Classic a trusted choice for musicians, sound engineers, and content creators looking for a professional-grade phone system.