Quad 989/2905 all around qualities

Do you feel like the ESL2805 have enough bass ?
I would expect it to be very similar to 988 and theoretically to 63 in the low end because they still use 4 panels (no extra bass panels, those only added to ESL2905 or 989)

To my ears they sound very, very similar in all respects. The 988 was an updated 63 with better electronics. I don't own the 63s but have heard them repeatedly. I have not yet had the chance to hear the 2905, unfortunately. Some people experienced quality issues with their late model Quads, but then again the earlier ones were not immune either to their foremost British design and craftsmanship flaws...

The big thing with Quads is they don't last forever, now with shops cashing in the their marketed reputation form years ago. They "someday" will need to be repaneled, keep this in mind because it's not cheap from a refurbisher, (despite being a simple and cheap precess that takes nothing more than a couple hours once your jig and expander/stretcher are in place).

Given the choice at this price point, I would buy the new Quads, 2805 or the 2905 (like I say, haven't hear this bigger model).

I felt that ESL63 doesn't have enough bass and not enough slam/dynamic range to play the rock to my satisfaction. And i am not talking about crazy SPLs or hard metal rock. That is the reason i am prompting to bigger (hopefully more dynamically and more bass oriented) 989/2905; The difference in price tag between 2905 and 989 is huge. It seems a common ground that 2905 is a better speaker than 989 (more refine, yet better slam and better bass), but it is difficult to measure whenever it worth the additional 3-4K$
That's why i want to start from auditioning the 989 and see if this direction will lead me somewhere. Probably i will found out that even with additional bass panels the results with rock are less to my test and that the difference with ESL63 is not that huge...

QUAD reliability problem is indeed an important point...

And I agree, the Quads squash (compress) dynamic range, and most of the music sounds like its at the same level all the time. I know exactly what you mean, not loudness, but rather the CONTRAST between dynamic crescendo and low level passages. SO many people mistake dynamic range with "loudness spl level". Anyhow, on another topic if you feel the urge to crank them and arc a panel by accident (it happens), be prepared to hand over up to $250-$450 to a Quad shilling tech for a repair- that's for one for one panel. And they are light in the deep bass department like many panels, and those that do go deep typically have moderate high distortion, with Sound Labs being the primary exception. There's no replacement for cubic displacement, as they say. But they cost alot.

There has been little advancement in speaker technology in over 30 years, be it dynamic speakers or panels. That's obviously reflected in the measurements and the subsequent sound. What has changed (when there actually is a change) is better average cabinet design, lower cost speakers that perform better than medium high priced speakers of the past, better average balance, and more uniform dispersion which is important in a reflective room. But, the good speakers and the Quad 57 and 63 that were good back then are still up on top today, with obvious normal maintenance. If the 2905 can be auditioned in the future and its doing it for you, it might be worth the freedom of re-paneling headache and questionable re-workmanship. If you find a good 989 that has been serviced and is packaged properly on a pallet for shipping (accept them no other way than on a pallet!) then this may offer perfect value.

You can add additional bass panels to virtually any stat and simply (well, its not that simple to do) extend the stators and charge the diaphragm off the same EHT output, size and panel number matters not to the hipot DC-DC converter. There are numerous routes here to take to get what you want, but let it be your ears that make the final decision.