I believe you will want your sub trim at +10bps on the Oppo.

On the sub, you will want to bypass the crossover since you will likely use the 950's bass management. The phase will take some experimenting. Once you get your SPL meter, take measurements of your frequency response, if you find a null, play with the phase to see if it helps it. It may or may not. If not, you may need to try different locations in the room for the sub to sit.

The volume should be under 50%, use the 950 trim to find the right level relative to your mains using the spl meter and test tones.

Have fun!

Thanks for the reply. I do have the sub trim at +10 on the OPPO but the HSU doesn't have a bypass per say for the crossover. It does have a crossover defeat switch which reads: "if you are using a subwoofer of LFE output, you can disengage the crossover by switching it to OUT. The crossover should be switched to IN when using high level inputs or two channel low level inputs." so since I have the bass management on in the 950 this switch should be set to OUT. Correct? Hopefully with this fine info I will get everything up, running and sounding great. I do love this hobby and especially upgrading. thanks again.

Sounds like you have it. I would agree on switching it to "Out" to bypass.

I have a quick question just to be safe. I have my OPPO BDP-83 set up according to Gonk's instructions (speakers set to large in 83, trims at 0, sub on) and have bass management turned on in my 950. Now I just bought a new Def Tech speaker system, Mythos 4's (l/r), Mythos 8 (c) and Mythos BPX for sides. In their literature they are recommending that if I am using a pre/pro or receiver with bass management and a separate sub (which I am) that I set all the speakers to small. Was just looking for a clarification on these two apparent opposing viewpoints (though I have had great sound quality with my system set up according to Gonk's recommendations). Hoping for a little peace of mind before letting things go here. thanks so much.

The small speaker settings should be set but only in the 950, not the Oppo. This engages the bass management in the 950 based on the xover settings also in the 950. The point being to have the Oppo pass the full signal via large speaker setting and then let the 950 do the bass management via small speaker setting. I hope this helps.

thanks for that tip. It seems that I was doing it right all along. Have always had the speaker settings in the 950 on small since getting the OPPO. I guess that's why it has always sounded so good. One other question that did come to mind, should all the crossovers in the 950 be left at 80 since that is what Def Tech recommends or can they be tweaked a bit. Never really clear on crossover settings for example if I was to set my center higher than 80 does that mean any bass under that number is sent to the sub? But I have to say, it sure feels good to upgrade after 15 years. The Def Techs sound so good (especially the BPX bipole surrounds; never had em before and listening to them was a totally new sound experience, at least for my non-professional ears). And for the first time I've experienced house rattling bass. Also invested in a Hsu VTF-2 MK3 and when I went upstairs while Cars was playing, rattling and rumbling were flowing through my kitchen. Sorry for the gushing but it's just a lot of fun to have the HT experience change SO much. And the good old 950 just keeps chugging along. Was seriously thinking about selling it to my sister for her basement but now I'm not so sure. It always is rock solid. anyway, thanks for the help, will be getting out the old SPL meter this weekend and testing.

Yes any thing below the crossover frequency will be diverted to the subs. With your Mythos Speakers, 80 should be plenty high.
Sounds like your having fun.
Keep on truckin'.

thanks for clearing that up. sometimes it can all be so confusing but yes, I am having fun and looking forward to watching my old movies (and the ones I just bought the last two days) on the new system. I noticed you have the Pioneer DV-47A. My first dvd player was the DV-47Ai which I still have in my living room (bought the OPPO 983H for my theater) but it's still a damn fine player.