I just bought a YBA Passion Integrated amp ($4,000US). A few months ago, Before buying this unit, I was looking into buying a YBA 2 AMP and preamp (around $6,000US). The integrated amp is a brand new model (it was released in December 01). Eventough the integrated is cheaper than the separates, it is BETTER sounding that the Series 2 seperates. If an integrated is well designed and well built, it can be as rewarding as separates without the extra cost. Remember that when you buy separates, you buy 2 transformers, 2 chasis... Also, you will have to buy an extra set of interconnects (beleive me it can be very costly task to find the right one). On the other hand, you have more flexibility when buying separates.
If you are on a tight budget and want the most bang for the buck and you are looking for new components, I would look into integrated. If you don't mind buying used, there are a whole lot more separates for sale on the market compared to integrated amps. The only reason why I bought a brand new unit is because the integrated I bought is a brand new model (I beleive it will take quite a while before seing this unit on the used market).
one more thing... When you buy online, you have no chance to audition the gear before you buy. If you plan on buying separates, make sure the amp/preamp are a good match. Buying without auditionning can be sometimes very deceiving. I would go around stores to listen to some gear. Make a choice on what sounds good to YOUR ears (not the salesman's ears). Once you choice is down to a few units, shop online for ONLY the units YOU auditionned. Remember, BE PATIENT when buying online. A good deal will come around sooner or later. The only way you will not be deceived is to ONLY trust your ears. Component reviews and other people's opinion are only there as guidelines. They are not to be taken as the ultimate reference.
One more thing, if you like tubes, YBA sound very close to tubes (but with solid state advantages).
Happy shopping.