Advice please on Wheels and Bottom Bracket

If I understood correctly he doesn't want a bottom bracket converter he wants a threaded BB he can use with the same crankset. That isn't possible as far as I am aware.  Factory installed BB30 bearings don't seem to last long though, mine lasted 1000 miles on the non-drive side but since I replaced it it has been fine for thousands of miles. 

For BB https://www.evanscycles.com/praxis-works-pf30-bb30-to-shimano-bottom-bra... and http://www.freeborn.co.uk/wheels-manufacturing-bb30-to-outboard-bottom-b... you just need to shop around for cheapest, i have both and well recommended.

Wheels mfg bb adaptor is the answer. And speak to a decent wheelbuilder like Strada.

BB recommendation: http://www.wishbonetw.com/product.php?fid=8&sid=19

One of these resolved all issues with my Campag Chorus cranks on a Cervelo R5 with BBRight, which is about as niche an installation as you'll find, so should be grand on a BB30/Shimano setup.

I weigh 100kg and suffered broken (rear) spokes regularly (1 every 6 months / 2500km or so). I had a rear wheel built with 36 spokes and only had 1 since (18 months / 7500km)

I weigh 100kg, never broken a spoke, buy decent wheels with 28 spoke count, Hunt etc. Hope do a bottom bracket convertor PF46 adaptor, you get different bearings depending on the crankset you have. It's simple to install but expensive to buy £80+

Don't know if it's much help, but on my training bike I've got a BB30 with an insert which came with a DA crankset and standard DA bearings. They've lasted for 5 years (30,000 mi) with very little maintenance.

I would recommend upping your spoke count to over 30 for both wheels, because it simply limits the potential for issues and then the grief if those issues arise. A friend is a former international prop, generally 120 kg and has ridden a 40 spoke back and 32 spoke front (recently the length of NZ) for several years without any problems. Used to break spokes on a monthly basis before that.

Buy some decent wheels, I haven't dropped below 100kg (ex league forward) for donkeys and can't remember the last time I broke a spoke. I've had over 180kg quite a few times over short journeys, this with a back wheel with a 32 hole Ultegra on open pro and a 36 hole 90s Sansin/Mavic Ma2 front, on top of the usual 100kg +loads daily for several years.

poorly built wheels is the problem not the number of spokes, I'd say forget replacing the spokes and just stump the money to get some decent factory wheels or handbuilt, my option would be the latter. You get to choose what spec you want, sure it costs more but a decent builder will have the tensions done correctly and use the right spokes for the job, you then shouldn't have spoke breakages except for extreme impacts.

As for the BB, this was one of the reasons I bought a CF frame with BSC threading, just cuts all the aggro out. There are some spendy ones out there but I don't have experience of such so can't make any recommendations.

I got some Mavic Open Pros made up by Harry Rowlands [google him], 36 spoke on Miche hubs - circa GBP250.  Utterly Paris-Roubaix-proof and very comfortabe.  Ideal for UK roads and probably the best GBP250 I've ever spent on anything to do with cycling...   

Think about a higher spoke count. Not only can it make spoke breakages less likely, it reduces the scale of the problem if it does. I'm not much lighter than you but have done plenty happy miles on 31 spokes and a couple of roadside tweaks of spokes adjacent the break!

Easily available replacement spokes might also be useful (not all modern wheels offer such a simple option).

I'm about 15kg heavier than you but had similar issues with snapping spokes...ended up replacing my rear wheel with one of Strada's "big fella" ones. DT Swiss RR511 rim, shim 105 hub although I think you can get dt instead. Absolutely bombproof, 18mm wide internally, comfortable & looks nice too. They do a disc version which I'm sure is equally indestructible.