A confession: I have about 20,000 CDs — and not one is a Led Zeppelin disc.

It’s not that I don’t want them; in fact, I used to own the whole catalog on vinyl. But once I purged those LPs, I realized I didn’t need to upgrade to CD — anytime I want to hear Zep, I can just turn on any rock radio station and wait a few minutes.

Still, every couple of years I get the urge to hear more than one Zep song in a row. So for a guy like me, you’d think the new anthology Mothership would be great. The only Zeppelin CD I need to own and all that, right? Well, yes and no.

Sure, the two-CD package delivers 24 of the legendary ’70s rockers’ biggest and best cuts, including the usual suspects like Dazed and Confused, Whole Lotta Love, Black Dog, Rock and Roll, Stairway to Heaven and Kashmir. And yes, every one is an immortal classic.

Trouble is, with a handful of exceptions, they’re the same two dozen immortal classics that were on the last two-disc Zep anthology — and the one before that. Worse, even a neophyte could reel off a whole disc’s worth of classics that aren’t here — like Living Loving Maid (She’s Just a Woman), Rain Song, Celebration Day, Dancing Days, Going to Calfornia, Fool in the Rain and Misty Mountain Hop, to name a few. But worst of all is that this anthology — like the one before, and the one before that — is completely devoid of bonus tracks. Even the DVD that comes in the deluxe edition consists entirely of footage from their self-titled 2003 video.

Instead of making their fans pay for the same two dozen songs every five years, here’s what they oughta do: Take all the albums, remaster them from the ground up, remix them for 5.1, expand each one with an extra disc of live recordings and whatnot, put them in a box and be done with it. Now that would be a Mothership.

Until then, we’ll stick with the radio. And with our new DVD copy of The Song Remains the Same.

The 138-minute concert flick from 1976 — which debuted on DVD back in ’99 — returns this week in a new Two-Disc Special Edition. First up is the original 11-song performance shot at Madison Square Garden in 1973. It comes with a newly remixed and remastered soundtrack in both stereo and 5.1 audio. If you’re a Zep freak, you might spot some sonic tweakery in tunes like Whole Lotta Love and Stairway to Heaven. If not, you’ll just know it sounds pretty damn good — good enough to balance out the absurdity of those self-indulgent fantasy sequences.

But what really tips the scales is the disc of new extras: Four more live performances from the gig (Celebration Day, Over the Hills and Far Away, Misty Mountain Hop and The Ocean) , vintage TV news reports about the tour and the theft of $200,000 from a New York hotel, an interview with Robert Plant and manager Peter Grant, and a 1976 radio profile by Rolling Stone scribe and future filmmaker Cameron Crowe.

It’s still not everything it could be — how about a commentary track, guys? — but at least it gives you something you haven’t already heard and seen before.