Thanks to everyone for their suggestions. I checked out the Naim forum and have read about ARO-cartridge relations there and elsewhere. The bottom line is that Downunder, Birdies, and No_regrets pretty much cover the topic. The Dynavector XV-1S comes out on top in these reports, followed by other Dynavectors. Lyra is also recommended but less so. I admire the XV-1S but as Birdies says its not much sweeter than the Troika I have. It's probably worth trying though.
People report success using a range of cartridges with the ARO. These include the Troika for which the arm was designed, and:
Dynavector XX2 Mk.2, Te Kaitora Rua, XV-1s (Naim forum)
Lyra cartridges (Stereophile review)
Ortofon MC20 Super II (Vinylengine user)
Benz Glider (Naim forum)
47Labs Miyabi47 (Naim forum): (geometry seems to be a good fit)
Linn:
**Everyone agrees the Troika is a good match. I have not found how far the stylus tip is from the mounting holes centerline, but measured this on my Troika to be roughly 7-8mm.
**The Akiva and other Linn cartridges do not get recommended often. Frank in May 07 Naim forum says: The top Linn cartridges are made by Lyra and I compared the Akiva to the TK Rua in an Aro when Peter did my set up last September - no contest, the TKR won by a margin in the Aro.
Dynavector:
**The XV-1S gets the most enthusiastic reviews as a match for the ARO. It weighs 12.6 grams so exceeds Naims recommendations for the 11gram arm; to use it one would need to get the heavy counterweight available from Naim, as No_regrets says.
**The Te Kaitora Rua is said to be good too: The geometry is not spot on with the TK Rua but it does not matter!! The music just flows! according to one Naim forum user. Its distance from mounting holes to tip is said to be 8.3mm. Downunder, I take it this has not been a problem for you? Another forum poster writes: I will reference the recent discussion on this forum where it was established that on the basis of pure measurements the Dynavector Te Kaitora Rua was also considered not appropriate for the Aro tonearm. This has not stopped many on this forum (and several dealers) to disregard this fact and use the cartridge on the Aro - and achieve wonderful results (as they have stated). Im afraid of mistracking and excessive and uneven record and stylus wear.
**The XX2 Mk.2 is said to be excellent for the price and a big improvement over the Mk.1.
Lyra:
**At 9.5mm the Titan distance to mounting holes is longer than in the Dynavectors or in the Troika. David Dever, a trade member (merchant) on the Naim forum, writes: The Lyra cartridges have generally been a fantastic match for the ARO, and should be quite suitable given their geometry (stylus tip to mounting hole centerline distance is between 7.5-10mm)from the Titan's description [quoting Lyras own description]: the distance from the center of the mounting screws to the stylus tip is 3/8 inch (9.525mm). Henceforth, all Lyra cartridges will be standardized with these height and mounting-screw-to-stylus dimensions. There's enough give in the mounting screw holes in the ARO headshell to make this effective distance shorter by a mm or sono problem placing it smack in the middle of the range, near to where the Te Kaitora Rua is already (8.3mm).
** The Skala is the one Lyra Ive likedothers have sounded thin or dry to me, in limited experience. According to Naim forum posts from June 2007, Jonathan Carr (Lyra's cartridge designer) said on the Naim forum that the Skala is much better suited to Linns Ekos arm than to the ARO.
There isnt much information on the Benz though some others agree with No_regrets that they work well on the ARO. Id like to hear more about that and also about the Miyabi geometry/synergy with the ARO.