ZDV CTLR EXPERIENCED OPERROR WHEN DESCENDING IFR ACFT BELOW MINIMUM ALT; LISTING SIMILAR CALL SIGNS AS CONTRIBUTORY.

Narrative

I WAS WORKING ZDV SECTOR 36 RADAR BY MYSELF. THE WX WAS MARGINAL IFR AND I BEGAN TO PLAN IFR APCHS INTO THE ARPTS IN MY AIRSPACE. I WAS WORKING 2 COMPANY ACFT; ACFT X AND ACFT Y. ACFT Y WAS INBOUND FMN AND ACFT X WAS INBOUND DRO. I CLRED ACFT Y OVER THE INITIAL FOR THE ILS INTO FMN AND WAS WAITING TO STEP ACFT Y DOWN REF MIA'S OF 10000 FT AND 9000 FT. AS I ISSUED A XING RESTR AT THE INITIAL OF 9000 FT; ACFT Y SAID HE COULD GET A VISUAL; SO I CHANGED THE CLRNC TO DSND AND MAINTAIN 9000 FT. SHORTLY AFTER; I ISSUED ACFT X A PLT'S DISCRETION DSCNT TO 9000 FT BECAUSE THE PLT HAD THE WX AT DRO AND WAS EXPECTING A VISUAL APCH. THE CORRECT ALT SHOULD HAVE BEEN 10000 FT. I THINK I CONFUSED THE IDENTITIES OF THESE 2 ACFT AND THEIR DESTS. I HAVE NEVER CLRED ANY DRO INBOUND BELOW 10000 FT (MIA) BEFORE THIS. I WAS THEN BUSY SETTING UP IFR APCHS INTO PAG; BDG; AND PSO -- RARE OCCURRENCES EVEN IN WINTER. WHEN I SCANNED BACK TO ACFT X; I REALIZED I HAD DSNDED HIM BELOW MY MIA. AT THAT MOMENT; ACFT X SAID HE COULD NOT GET DRO IN SIGHT AND REQUESTED AN ILS. I IMMEDIATELY CLBED ACFT X TO 10000 FT AND AT 10000 FT BEGAN VECTORING FOR A STRAIGHT-IN ILS. I WILL NOT ALLOW THESE SIMILAR CALL SIGNS TO CAUSE CONFUSION OF ACFT IDENT/DEST IN THE FUTURE.