Contents from the former couple's Pasadena mansion are now up on the auction block, helmed by John Moran Auctioneers ... which is hawking any of the goods in an effort to pay down debt owed in Tom's bankruptcy case.

There's a lot of stuff they're trying to unload here ... everything from furniture and décor to valuable art pieces and sports memorabilia that have graced Tom and Erika's home for a long time.

Here's some of the most valuable items up for grabs -- the biggest ticket item is a 1997 Steinway piano that's expected to fetch anywhere between $40,000 and $60,000. The auction house says it's a rare edition, and considered one of the finest instruments of its kind in existence.

There's also mid-century art from guys like Joan Miro and David Hockney -- paintings and etchings that could rake in thousands of dollars on their own -- plus a few Glenna Goodacre bronze sculptures ... one of which is valued at between $30k-$40k alone.

Other things being sold include ... Girardi's personal library, which includes his own personal law books, rugs, wall mirrors and a variety of sofas and lamps. They could all bring in a haul of tens of thousands of dollars combined, if not more.

The court-ordered sale is scheduled to get underway on September 21, starting at noon.

This is a place that Erika was once proud to show off on camera -- she's given a tour of the Pasadena estate -- but, of course, her ex-hubby has fallen into trouble with the law ... as authorities have alleged his old firm mismanaged tons of client assets for their own use.