As expected, “Superunknown,” the fourth album from Seattle grunge pioneers Soundgarden, enters the SoundScan album sales chart in the top position this week. According to figures provided by an industry source, the collection, a favorite among insiders since advance tapes began circulating in January, sold more than 162,000 copies.The group’s previous A&M album, “Badmotorfinger,” sold more than a million copies in the U.S. Soundgarden plans to begin an American concert tour, its first as an arena headliner, in June. Following in second place is “The Downward Spiral,” the new TVT/Interscope release from industrial titans Nine Inch Nails. Created almost entirely by group leader Trent Reznor, the album sold nearly 119,000. Following a recent surprise show in Los Angeles, Nine Inch Nails begins touring the States April 17 in Seattle, arriving back in L.A. April 26. Braxton slips Last week’s No. 1, the debut set from R&B singer Toni Braxton, fell to No. 5, but her dual wins at this week’s Soul Train Awards will probably push the album back up the chart next week. After a respectable debut at No. 12 last week, “The Funky Headhunter,” the Giant release from newly hardened rapper Hammer, drops to No. 22. The DGC debut from acid-folk singer Beck, “Mellow Gold,” also in its second charting week, jumps from its No. 15 entry to 13. “God Shuffled His Feet,” the latest Arista issue from Canada’s Crash Test Dummies, crashes the top 20 for the first time, at No. 17. New age powerhouse Largest sales gain of the period was turned in by new age star Yanni, whose current Private Music project, “Live at the Acropolis,” moved from No. 55 to 26 in its second week, with sales jumping from 20,000 to 44,000. Among the other new entries: “Hard to Earn,” the third Chrysalis set from street rappers Gang Starr, which arrives at No. 25; “Brutal Youth,” the latest Warner Bros. effort from Elvis Costello, featuring a reunion of his original backing band, the Attractions, at No. 34; “Your Filthy Little Mouth” (Warner Bros.), the third full solo release from former Van Halen vocalist David Lee Roth, at No. 78; and “Martinis & Bikinis,” the latest Virgin album from soulful femme rocker Sam Phillips, at No. 182.