I also started with a Pulse 8X originally. Great machine, found a lot of cobs with it in Jupiter. I switched to the AQ1B for greater durability, and better detection of smaller non-ferrous targets. Many times, a Pulse Induction (PI) detector will not see a gold chain with small links. PI works by emitting a pulse which in effect "charges" any metal objects under the coil. Then the detector senses any remnants of the charge held by metallic objects. Gold and silver (being very good conductors) loose this charge very rapidly. Tiny gold parts (like links in a tiny chain) loose this charge very quickly, sometimes before the detector can even sense it. This is why very small gold and silver objects are sometimes missed by PI's but found by VLF detectors like the Minelab's. Put a pendant on that necklace and any detector will see it. Aqua Pulse detectors are much better than other PI detectors in this area, which coupled with the increased durability is why you see them on most of the serious professional treasure hunting boats.
As far as accessories go, Aqua Pulse has 8", 10", and 15" coils, plus a 12", 36", and adjustable/extendable probes. We also offer large boat-towed coils and custom accessories to fit your needs.
Jolly Mon - I wouldn't get in too big a hurry to upgrade your AQ1A. There is little difference in functionality between the two. The upgrade extends the battery life, and makes my life easier if it should come in for repairs by adding chip sockets instead of having the IC's soldered to the board, etc. As far as improving the effectiveness of the detector, not too much has changed and your unit will still out-perform many current PI detectors.
I have used just about every metal detector on the market in real world situations. All detectors have their strong points, but in my opinion the Aqua Pulse has the best blend of function, options, and durability. Before someone asks, I formed that opinion long before I joined the Global Marine Exploration team and became the sales and service agent for Aqua Pulse USA.
Jason