Hi everyone!
It IS possible to have an all digital system with 4 or more Bl5s. I use a Tascam digital monitor controller (DS-M 7.1) which works really well with the BL 5s. Although longer made, you can occasionally get one on e-bay. Currently I use 5 Bl 5s, and they are very satisfying for both music and cinema (a Beolab 5 center channel is simply stunning, and has led me to reconsider the nature of stereo!).
About the alleged datedness of Bl 5s (this month is the 10th anniversary of their introduction!), they are still at the forefront of loudspeakers. At Sausalito Audio, we have been surprised that there has been no serious attempt to improve on their performance by the competition. They remain a uniquely effective and viable product, and seem likely to remain so for quite a while. Concerns about resolution of the input signals are really minor, especially given the other virtues of the design.
So, don't fret. The Beolab 5 is still at the absolute forefront of audio. My partner thinks it may be the best and most important audio product ever made.
Best regards.