I made a similar thread in the Gantz forum.

If the anime continues someday and has more episodes (the upcoming OVA is a start) and Funimation dubs it these are my choices for the new characters.

I've been reading the manga so I've gotten a good sense of their personalities.

I've also taken physical appearances into consideration and matching suitable voices to them.

My choices are also based on listening to work the VAs have shown in other dubs.

I've also selected VAs in the Texas area and VAs who have actually worked with Funimation in the past (being more realistic) and tried to avoid multiple-casting.
If a VA voiced a notable character in the first anime series I excluded them for new characters. VAs who only voiced minor characters, or were additional voices in the first series, or haven't worked on the series at all were eligible.

but first the reprisals of course

Returning Characters and VA Reprisals for the Yomi and Yami arcs:

Ryozanpaku:
Kenichi Shirahama – Josh Grelle
Miu Furinji – Carrie Savage
Hayato Furinji – R. Bruce Elliott
Akisame Koetsuji – Kent Williams
Shio Sakaki – Chris Sabat
Kensei Ma – Vic Mignogna
Apachai Hopachai – Sonny Strait
Shigure Kosaka – Trina Nishimura
Tochumaru – Chris Cason

Shinpaku Alliance:
Haruo Niijima – Todd Haberkorn
Takeda Ikki – J. Michael Tatum
Ukita Kozo – Mike McFarland
Kisara Nanjo – Colleen Clinkenbeard
Natsu Tanimoto (also a member of Yomi, disciple of Sougetsu Ma) – Eric Vale
(Jason Liebrecht was the original voice but was replaced after a motorcycle accident which prevented him from voice acting for a while, at this point it makes sense to stick with Eric Vale who IMO is better anyways. Eric did mention in an interview that he feels bad for taking over the role but had a lot of fun playing this character)
Seigfried – Chris Cason
Thor – Bob Carter
Freya – Stephanie Young
Shiratori – Joel McDonald
Matsui – Zach Bolton
Kamioka – Eric Cherry
Mizunuma – Chris Burnett
Kurokawa – Bruce Lewis

Kenichi's Family:
Honoka Shirahama – Cherami Leigh
Mototsugu Shirahama – John Swasey
Saori Shirahama – Cynthia Cranz

Koryou High School:
Yuka Izumi – Brina Palencia
Makoto Himeno – Kristin Sutton
Ono – Caitlin Glass
Yasunaga – Greg Dulcie
Chihiro Takashima – Leah Clark
Shimayama – Daniel Katsuk
Tanaka – Orion Pitts
Daimonji – Chris Ayres

Other Significant Returning Characters:
Ogata Isshinsai / Sage Fist – Jason Douglas
Ryuto Asamiya (member of Yomi, disciple of Ogata Isshinsai) – Jerry Jewell
Renka Ma (Shinpaku Alliance member) – Kate Oxley
Hakubi / Ryo Ma – Barry Yandell
Shinnosuke Tsuji – Chris Rager
Sogetsu Ma (member of Yami's One Shadow Nine Fists, Master of Natsu Tanimoto) – Rob Mungle
Loki (Spy for Shinpaku Alliance) – Travis Willingham
Number 20 (Spy for Shinpaku Alliance) – Monica Rial
Berserker (in-training disciple of Ogata Isshinsai) – Rob McCollum
Ryu Genson – Cris George
Shokatsu Kouan – Jon Duckworth
Kaede Tanimoto – Brittney Karbowski

*the following list of new important characters is organized based on the order in which they appear in the manga (and I assume the anime would follow as well), if you want to see pics of the characters or learn more about them I suggest MyAnimeList.net or kenichi.wikia.com

Inspector Honmaki – Mark Stoddard
Christopher Eclair (Yami Assassin) – Illich Guardiola
Shigure's Father (flashback) – John Burgmeier
Hachirobe Kosaka (Shigure's adopted father) – Grant James
Raichi Li (member of Yomi, daughter of Li Tenmon) – Lindsay Seidel
Tenmon Li (member of Yami, father of Li Raichi) – Cole Brown
Sho Kano (Leader of Yomi, disciple of Akira Hongo) – Johnny Yong Bosch
Akira Hongo (member of Yami's One Shadow Nine Fists, Master of Sho Kano) – David Wald
James Shiba (Boxing Master of Ikki Takeda) – Andrew Chandler
Boris Ivanov (member of Yomi, disciple of Alexander Gaidar) – Sean Schemmel
Alexander Gaidar (member of Yami's One Shadow Nine Fists, Master of Boris Ivanov) – John Gremillion
Radin Tidat Jihan (member of Yomi, disciple of Silcardo Jenazad) – David Matranga
Sham – Majken Bullard
Shizuha Furinji/Miu's Mother (flashback) – Shelley Calene-Black
Silcardo Jenazad (member of Yami's One Shadow Nine Fists, Master of Radin Tidat Jihan) – Troy Baker
Rachel Stanley (member of Yomi, sister of Ethan Stanley, disciple of Diego Carlo) – Jamie Marchi
Ethan Stanley (member of Yomi, brother of Rachel Stanley, disciple of Cyril Rahman) – Jeremy Inman
Diego Carlo (member of Yami's One Shadow Nine Fists, Master of Rachel Stanley) – Patrick Seitz
Fortuna (member of Yami, Host of DofD tournament) – Brian Mathis
Jennifer Grey (FBI agent, "fiance" of Sakaki) – Kara Edwards
Spartacus (adopted son of Fortuna) – Jonathan Brooks
Tsutomu Tanaka – Michael Sinterniklaas
Chikage Kushinada (member of Yomi, disciple of Mikumo Kushinada) – Tia Ballard
Kajima Satomi (new Leader of Yomi, disciple of Saiga Furinji) – Andrew Love
Tirawit Kokin (member of Yomi, disciple of Agaard Jum Sai) – Justin Cook
Cyril Rahman (member of Yami's One Shadow Nine Fists, Master of Ethan Stanley) – Charles Campbell
Mikumo Kushinada (member of Yami's One Shadow Nine Fists, Master of Chikage Kushinada) – Lydia Mackay
Agaard Jum Sai (member of Yami's One Shadow Nine Fists, Master of Tirawit Kokin) – Duncan Brannan
Saiga Furinji/Miu's Father (Leader of Yami's One Shadow Nine Fists, Master of Kajima Satomi) – Dameon Clarke
Chou Enshin (Yomi before Hermit defeats and replaces him) – Blake Shepard
Jisei Ro (Chou Enshin's master) – George Manley
Danki Kugatachi (Freya's grandfather) – Bill Flynn
Rimi (in-training disciple of Ogata Isshinsai) – Luci Christian
Hajime Suzuki (deceased friend of Shio Sakaki and Akira Hongo) – Charles Baker
Radin Tidat Lona (sister of Radin Tidat Jihan) – Nazia Chaudhry
Lugh (in-training disciple of Ogata Isshinsai) – Leraldo Anzaldua

*Edit*
Added more characters, now up-to-date with the manga!