Walt,
As reckstar24 had mentioned earlier don't beat your self on getting D-211. It is by no means a vintage PCDP with a so so headphone out and I don't think that you had wasted your money at all. I have mines and will not part with it. There are times with certain music when I don't want all the detail or huge soundstage from the DCP-150. Times like these I want a PCDP that will deliver enough slam and detail to make listening fun and not critical. The D-211 fits this bill perfectly, besides with the price you pay for a DCP-150 you can purchase 3 complete D-211 with original box and papers. The D-211 next to the D-311 IMO are the most detailed and accurate sounding vintage PCDP in Sony's line up, with the D-211 as mentioned by many having a better headphone out of the two.
Everyone has their opinion on which PCDP has the best headphone out, I own a DCP-150 and the opinion stated by me is mines alone. Someone else who owns a DCP-150 and D-211 may have a different opinion than mines and that's fine. What really matters in the end is that you have found a PCDP that has good sounding headphone out and one that is well within your budget. No sense in pouring all your money on a DCP-150 if in the end you feel the sonic qualities between the two isn't worth the price difference.
As for the level of headphone out difference between the D-211 and DCP-150 I would say both have about an equal amount of slam with quite a bit of bass. As far as the level of detail, accuracy, and soundstage I would say that there is a major difference between the two with the DCP-150 being the better of the two. The level of detail, accuracy, and soundstage out of the DCP-150 IMO approqaches that of fullsize CDPs. The DCP-150 is the only PCDP that I've heard so far that sounds nearest to a fullsized PCDP, however it doesn't by any means surpasses it in sound quality. It just narrows the gap between the PCDPs and fullsize CDP more than any other PCDP that I've had the opportunity to listen to or own.