Driving the kt88/6550 in set mode

[duderduderini]

Hey Guys.
My mate the amp builder guy has built an amp which at my place sounded marvellous.. I have another Mate who really needs to get into tubes cause he loves jazz et al, so I took this amp over for him to listen to. Well blow me down if the amp was distorting as if it where going into overload. At my place we used one of my marantz cd50's at full volume(on its variable output) with no prob but my other mates CD player is a NAD 521 with fixed output.
So i ring the mate who built the amp and I asked him if his driver stages could be contributing to this....
Input signal goes int 6n1p then el84 in triode mode then driving the pair of kt88's... to which he says no and anyway thats cool with me cause I will go another way with driving these tubes(when I build mine I just got all the iron)
So I can understand why you would need a 2 stage affair to get a 300 b working given its impedance and p-p voltage requirements but do a pair or a triplet of 6550's in se mode really require this much drive?
I dont get it... the 6n1p amplifies the voltage but my friend then says the el84's provide the current to drive the kt88's.
So anyone can join in here, not to cure my friends amp woes, but to explain to me a) why cant a D3A in srpp lets say provide enough drive for a pair of 6550's? and if not can someone explain (with pictures.. you wont insult me) the difference between a single driver tube approach and why do we need to actually provide a "current source" as my friend describes it.
I think he is just driving his power stage too hard but then again he loves that glassy sound...
So what do you guys think?