You're welcome. That is a relatively small listening room, so you likely wouldn't need much more power than the 335 or a comparable AV receiver unless you plan on running at close to reference level (-20 and lower) for extended periods.
Though many 8 ohm nominal speakers can dip down to 4 ohm for short periods, I wouldn't feel comfortable taking a chance on running the Monitor Audios on solely the HK. These speakers are well reviewed and seem to be a pretty nice option, but unless you had a stronger AV (HK 635, 7300, Denon 3805, Yamaha 2500, Onkyo 703, etc.), you'd likely be stressing your 335 w/the MAs at higher levels.
Have you listened to these speakers yet? The reason I ask is that speaker choice is very subjective and if you have the opportunity to listen to these as well as others in their price range, you'll be able to determine the best fit for your system and budget. If you found some similar options that were a bit more sensitive, I would opt with an 8 ohm, higher sensitivity speaker, possibly something else from MA may suffice. If you find these are exactly what you want, you may want to consider a receiver upgrade or as I mentioned and external amp.
If you have the space, the amp is most definitely the best way to go. If not or you'd like to keep everything all under one umbrella (e.g. AV receiver), I would condsider one a bit more robust in the amp section. The HK may work just fine for your scenario with the MAs, but I wouldn't feel comfortable running them w/the 335s close to reference level, plus I think you'd likely be impacting the performance of the MAs doing so, thereby missing out on their true potential... -TD