In my mind, the changes to help the system out would be:
Replace Onix XCD-88 CD player, maybe with the EE tubed CD
Replace Onix SP3 with something even more "tubey" like the EE M520
Go with higher power, like the Butler 5250
Add preamp, tubed or not or drive amp directly from CD player
Try out a combo of these with the existing speakers
Try new speakers with larger driver(s)
Add sub(s)
If I'm reading your post right, you are using the SP3. That is aoubt 40wpc of tubed sound. The SP3 is an integrated so you won't want to add a preamp into the fray.
Checking some of your recent posts, I see you just picked up a full Odyssey speaker system for your HT. First thing I would do is move your Loreli's into your 2 channel system and see if these give you the sound you are looking for. If they are, then you can deal with the amplification as a secondary issue. If the Lorelis don't provide the bass you are wanting, then the only answer is a sub. While you are at it, I'd roll your Nightingales into the system also just so you have another point of reference.
If the Odysseys fit the bill but now you can't get enough SPL's due to the Onix's 40 wpc, then you need to start looking for a new amp. First you have to ask yourself, do you want to stay with tubes. A quick way to check is play the same CD (in two channel mode) on both of your systems. If you can't live without the sound of tubes, then you need to start looking at some high powered tubed integrated (or separates). If you want to go back to solid state, you have a myriade of choices. I'd start by calling Klaus back and getting a Stratos. Remember, he's got a 30 day in home guarantee.
On the tube amp side, large integrated's should be fairly easy to find (new or used). Again, you have a fairly large choice, Cary, ASL, Audio Research, and many more.
If you want to keep your Onix amp and just upgrade your speakers, you now have a limiting factor. You choices have just narrowed emmensely. Your speaker search should be for something as far above 90dB as you can get without going to a single driver speaker. Reason I say that, most single driver speakers need some sort of sub below them to fill in below 50Hz (don't blast me here guys, remember, I'm an SET/Lowther owner/fan). Where I'm pointing you is towards something like Audio Note Speakers. they are generally above 90dB, very tube amp friendly and have damned good bass for Rock. Being a transmission line speaker (amongst other reasons) they show a releatively flat impedence load to the amp. They offer them in kit form if you wish. If you don't have a AN dealer around you, David Cope of Triode and Company is very easy to deal with (he is the distributor).
I suggest AN because I have personally played with them specifically with a 40 watt EL34 amp. The system was great with rock. They may be just what you are looking for. They sort of sound like a little version of the Loreli's.
