New op amps, good idea?

To further Al's point, some makers are using NOS parts because they feel they are better for their particular application. Also a design may have been optimized using certain parts and the substution of "better" ones may destroy the balance achieved by the original ones. I have read several accounts in the modifiers forums of how after extensive modification with expensive replacement parts the owner returned it to the original state as being better. As Al points out new caps of the original value are the safest path to begin with.

Great information so far and exactly why these forums are so helpful and appreciated. Yes, it is an Apogee Dax, but not the one pictured with my previous Mini Grands. I have Duetta Signatures now and the one we're discussing is an original Dax 1.
For those of you understandably unfamiliar with Apogee speakers there were 2 models of Dedicated Active (electronic) Crossovers (DA?X?) (actually 3 were supposedly developed but only #'s 1 and 2 really hit the market) which were designed to "divert around" the passive crossover components built into the speaker and act as true control centers of the woofer and midrange/tweeters as well as facilities for matching gain of different amplfier outputs when running the speakers bi-amplified (a REQUIREMENT when utilizing the Dax).This 'specialization' for only a specific few of the Apogee models is what makes it such a lure to those model owners. Over the years the Dax 1 [in the old Apogee forums] began as 'the cat's meow' for an admirably long time but with the advent of newer crossover designs by other companies (though none were ever specifically designed for any one particular brand or speaker model to the extent that the Dax's were for Apogee), other crossovers began to replace the now-aging Dax's... I myself have been using an excellent example of exactly what I'm saying: I've been the very happy owner of an NHT model X2 active crossover which is currently doing duty splitting my full range preamp output at 50hz into my Rel subwoofer and then [through the use of an 'rca splitter' on the high output jacks], sending the remaining signal to a dedicated woofer amp and a dedicated mid/tweeter amp into the [bi-wired] passive crossovers....(note there is no control for matching separate amp outputs but I've been fortunate that there seems to be a good balance overall).
The Dax 1 will add tremendous flexibility and I feel will make a worthy addition IF I can get it to today's high standards of transparency, dynamics, and all the other assets sought after in a well designed quality crossover...
Thank you for all your thoughts and suggestions so far, as I said, these are exactly the discussion points I need to have with the technician... Now all I have to do is figure out where I draw the line on the law of diminishing returns when it comes to deciding the $$$ expenditure on this. Certainly, I do realize I'm pretty much marrying this unit and I have no problem with that idea at all IF it turns out to be as good as I hope.... For the record, while not one to throw dollar figures around on these forums I will say that the unit originally retailed for $4K and that I have an 8/10 condition which I paid just under 25 cents on the dollar for... Which leads to the question inspired by Bombaywalla's excellent list of specifics above (thank you!): how much should / could having all/most of the above cost????? This hobby is relentless.... Thanks again ,everyone.

I also have DSs, one currently needing repair. I am eventually going to upgrade them with better wiring and binding posts and eventually a better base. I have RELs myself but I doubt you will need them with the DSs. I had large subs when I was using them last and never felt the need to add them. Have you been on the Apogee users forum, it is quite helpful? I run my RELs off the power output of the amp, have you ever tried this?

This is the one I meant, you said you had been on the old ones previously.
http://www.apogeespeakers.com/

Just for some reading material....
I've built a CMOY pocket headphone amp.
I used the OPA2134 series.

http://tangentsoft.net/audio/cmoy-tutorial/parts.html#op-amp

Somewhere in the documentation is a long list of opamps and how the author feels about them. Some are very good while others have audible flaws which some may find acceptable, others not.