Building a solid wall of barrels relies on a router as noted above. No other way to do it really due to the limitation on input. Using the mods currently in FTP the router is one of the few options. However realize that it can be flooded fairly easily by several quarries running at once so for large operations have the materials deposited into a chest, a router extracts from chest for a given back of barrels, ejects into the other router who then inserts. If you keep rows/barrel types in some conformity so a given router isn't handling a ton of variances this stacks stuff up nicely for it and lets it keep up. With some work with the pipes/chests and input handling you can set it up to handle N quarries where N is about 5/ender chest and one set of routers per row per ender chest. Minimal to no real lag noticed by me either. After enough inputs the BC pipes just become a solid stream of goods so it even stops really adding to the graphic lag from objects in motion. The downside to this design is getting stuff back out in scale. It's one thing to run around smacking chests, it's another to do it to pull out all the mats for 10 advanced hybrid solar panels. I gave up on creating an intuitive system to pull from a storage facility of the scale I do.
I had built one in RP2 tubes and like but tore it down. It dragged down my system unacceptably (32G ram, I7-3960) when I scaled it up to handle a max of 655,360 of each raw mining resources. After the 10th quarry came online it just didn't go well for it and never could overcome it very well within the design limitations (I keep everything in a 128x128 square maximum). Also took a great many machines to handle the input scale but that was workable which necessitated a lot of its special energy creation. When you have the room for it that's not a big deal in of itself but needed a lot running around. It finally became a CPU crisis as it checks its routes repeatedly as objects travel. Pulling stuff out was a bit of a pain to set up in my opinion. Also had to think very carefully about the piping to avoid loops and stuff going where it shouldn't due to the need to reuse colors.
What I've taken to doing is adding logistic pipes and putting a Chassis mk2 above each barrel. Then I just alternate barrel with pipe as high as I need (I use 4 rows so I can reach any barrel manually if needed). The pipes take care of inserting into the barrels below them and there is an extractor that'll pull out from the bottom no matter where it is connected. It used to exhibit the same CPU costs but the current version seems to be holding up so far. I haven't finished getting it fully operational though so it may have the same scale issues. So far though it's had far less cpu impact for the rows (40 barrels per side, 80 in a 2x10 row with 15 row sets with 2 wide aisles between them) than the tubes did in a similar configuration with the paint path restriction system. This lets me put everything into a large warehouse like room that is 10 high (my standard for a single floor). I'm hoping to go to field trials with this design in a week or two. I have high hopes of it handling at least 10 quarries per ender chest drop box from a single entry point into the system and would like to see it handle 40 quarries total at time without impacting my computer out of acceptable ranges.