Albert,
I use pure sphagnum (usually Chilean) for only a small handful of Paphs myself. I water with Chicago tap water, 225 ppm total disolved solids. Paph purpuratum and Paph purpurescens (sensu Fowlie) which is sunk into Paph virens without explaination by Cribb. Both of these plants have been in moss for over 20 years.
There is a grower in the Chicago area that grows 100% of her orchids in NZ or Chilean sphagnum. Paph rothschildianum, bellatum, lowii, druyii, armeniacum & mastersianum are some of the plants she has bloomed and I have personally seen in bloom over the last 25 years. You absolutely can grow all Paph species in nothing but sphagnum. I have seen it done.
A couple tricks she has shared;
*Key, wet the moss before you repot the plants. The old moss is easier to get off the roots if it is wet, the new moss must also be wet.
*Also very important is that you pot the plants loose. DO NOT PACK the moss in tight. Particularly for the paphs, keep the moss loose so that it will breath easily. Packing the moss too tightly is the reason many people fail over the long run growing in sphagnum. By loose I mean when her plants are freshly repotted often the plant is still wobbly, she will even add a few bamboo skewers to hold the plant up until the new roots prop the plant up better.
*Each plant will have a very different watering schedule versus what its schedule is when in bark. She lets her Paphs get fairly close to dry, her Phrags she waters twice as often as the Paphs, keeping them much wetter.
Generally plants in sphagnum will go much longer than similar plants in a bark mix in the same location. That is the reason she went with sphagnum. She likes to take week long trips and does not want to have to have people coming in to water her plants. It has worked well for her over the last 25 years.
So give it a try, it can be done. The key is to observe your technique and see how the plants respond. If they seem to rot, repot them into fresh moss and experiment with keeping the moss looser in the pot.
Go for it
Leo
) or 2.25" pots with varying amounts of NZ sphag in them. Not that I can claim to have grown many plants from this stage yet, but for just out of compot Paphs I put them in pudding cup pots with maybe half and half NZ sphag:CHC with some charcoal sprinkled in. When they get potted up to a 2.25" pot in 6 months to a year I lower the sphag to maybe a quarter of the media, and then after a year there, if they haven't outgrown the pot, I repot them into a new 2.25" pot with out sphag. Pots larger than that get no sphag and some smaller aggregate chunks (LECA of some sort), larger still get larger CHC and larger LECA...you get the idea. The reasoning I have behind this is that smaller seedlings seem to benefit from a little bit higher and more even moisture level, and smaller pots dry out faster as well. By potting up each plant in my still-too-small collection by grabbing a handful of this and a handful of that to customize things, I feel like it gives me more predictable drying times. The other upside to using the sphag only in the smaller pots is that seedlings are (hopefully) growing faster and in need of potting up more frequently, so I don't have to worry about the 'when is the mix sour and in need of change' issue. I've also found that sphag in larger pots leads to more algae - probably also a function of more mature plants growing in higher light and staying wet longer in larger pots - since I grow everything in clear plastic. The clear allows me to see the happy new roots weaving in and around the sphag, so it's worth a little algae to me! I know I talked about more than just sphag, but I didn't think I could paint the picture without it! 
