The congestion you describe may be a function of several things: first, the Quads cannot really reproduce the 'scale' of a full orchestra at full swing with real conviction, dynamics and authority. Yes, they are beautifully coherent, and will produce bass if properly set up, but I have never found them to provide the deepest foundation that is essential to a convincing presentation of large scale music or the dynamic swings associated with it. (Mind you, my long, long experience is with a pair of Crosby Quad 63's that I have owned for decades, not the same as the 998's, but I suspect that there is not a huge difference). I don't think its a question of a bigger amplifier- the Quads seem to be very happy with smaller amps (I had great success in the day with an ARC Classic 60 and would suspect that Quicksilvers, Jadis, or other more 'modern' tube amps would give you almost all their performance).
THe other area where potential 'congestion' may lurk is in the front end- I have gone thru a serious set of upgrades in the last 4 months- from Well-Tempered TT and ARC SP-10 to Kuzma Reference and Triplanar to Kuzma XL and Airline, all using a high-end Lyra (Parnassus, now Titan i). The change is very dramatic- the Well Tempered is musical but frankly, a little 'light'; the change in phono stage to a Steelhead, and a more modern but still 'musical' line stage- Lamm 2- has brought the front end up to very authoritative standards.
Finally, I don't know how much all those improvements would have changed my own view of precisely the congestion you are complaining about, since I made the very dramatic change to a horn based system. In fact, I had some of the same complaints you did about image congestion, and having gone through what amounts to a complete change of system (I still have all the old equipment, including the Quads), I can tell you that the combination of serious front end plus horns makes this a non-issue. ( At least most of the time- there are recordings that are still far less big and open than others but i can now, with a decent recording, produce the scale, dynamics and authority that I couldn't reproduce with the Quad).
