Decided to place JBL 2245 18" sub in the lower compartment of the A5-7 cabinet as a built in subwoof. Once you separate the MR horn with the 515-8G driver from the remaining cab you have about 7+ cu ft which when fiberglass stuffed gives about 9+ cu ft. This is adequate for the JBL which is then tuned to low 20hz via vents and then XO to the MR horn at 175Hz. Best of all
this mod does not require any cabinet cutting only the already needed stiffening of the cab. Unfortunately injured a leg and been unable to complete the job and do listening tests but will report back ASAP. This mod along with a tweet above 7-9K will correct the two acknowledged weaknesses, that is extreme lows and highs. Off hand I do not know of a single cab speaker that can match it's potential capabilities.