You are running up against Denso's last-century web-presence and 19th-century like distribution system.
I can't even find a -2006 for sale. The -2003 RA lists is same size/spec as all the other listings for that engine so would work. I'm guessing the Denso web-site you checked is still listing the ORIGINAL filter size they spec'd for that engine a decade or more ago - the J engine has been around since 1996. In the last 10 years, most filter manufacturers have discontinued a lot of filter sizes in favor of just one smaller size that will fit multiple prior applications, but still with the same flow and bpv settings. I'm going to guess the -2003 is the replacement spec for the -2006, and the -2006 is just old info their after-thought corporate web info is still showing.
I went through this a while ago trying to find the original, good sized, high-media filters for a '90s Acura. Since these use m20x1.5 threads, you have fewer options than say a Toyota, which has 3/4x16 studs and thus can poach from the larger US domestic sized supply chain/options.
The Denso filters are quite good and I like them, but I've given up on sourcing them easily and often use Wix, Bosch premium, or Motorcraft "S" line which are pretty much fully equivalent in quality, etc. Also, I can only get the new, smaller spec ones in Denso, so I am using larger size Motorcraft and PureOne filters on our Lexus and Acura now.