Six From Sirius v.1-2

Six From Sirius #1 – 4 (1984) : The galaxy teeters on the brink of catastrophe as the two worlds prepare to do war. In a desperate bid for peace, the worlds agree to hold talks—but a key ambassador, a telepath known as Phaedra, has been kidnapped by forces wanting to sabotage the peace process. To avert Armageddon, the galactic federation known as Sirius Swarm sends a team of crack troubleshooters to rescue her. But what begins as a straightforward mission quickly turns ugly as a strange collection of foes tries to stop the six from rescuing Phaedra.

Six From Sirius 2 #1 – 4 (1985-1986) : Following the treachery that ended their last mission, the Six from Sirius are returning to Sirius Hub to tender their resignations. The six had been branded as traitors, though, and are intercepted on their way back to the Hub. There they are sentenced to prison on the strange world called Planet-X, where once an entire race disappeared into thin air before they could be overrun by invaders. Speculating that they had found the key to dimensional travel, archaeologists now seek to discover that race’s secrets.

When a mercenary band called the Ghost-Makers attacks Planet-X, the heroes manage to escape from their prison—and step through a strange portal into another dimension. There they encounter the descendants of the race that had previously stepped through the portal, and suddenly, they find themselves now menaced by dangers from both dimensions.