If the Hawke is rated for spring-piston air rifles I'd contact Hawke once you know for sure the scope is the problem (I just did an article on this in the Mar/Apr WCT where I discuss Barrel Droop). Other issues with the spring-pistons could be with the mounts and/or the mounting screws coming loose from the stock/barrel (I've had this happen on several spring and gas-piston guns). As for the other optics on the market, I'm not aware of any that has been "spring-piston" approved by reliable shooters but that doesn't mean their isn't something out there. Like you, I need the magnification and with the arch an air rifle produces I wouldn't feel comfortable using a laser as being off by just a couple of feet could result in a miss.
All PCP rifles will be scope friendly. The Discovery is rated as an excellent air rifle but it has a lower air reservoir capacity (135cc) and can only be charged to 2000 PSI which makes it every easy to fill with a hand pump. Unlike the Marauder series, it can also be configured to use CO2 and has a rating of 900 fps with air. I'm considering getting one in .22 specifically for birds in buildings due to the number of repeating shots and ease of filling.
The next step up would be the Marauder Pistol. It has a much smaller air reservoir (65cc) but a higher fill rating (3000 psi) but the velocity is only rated around 700 fps. While the velocity is much lower (mine is averaging 647 fps) than a Discovery, it is still very capable of taking out birds out to 30 yards (and might be safer in buildings) and is also very easy to conceal as it is more like a carbine with a stock attached.
I agree that neither of these will most likely approach what the RWS 350 Mag is capable of doing, so if your looking at replacing it with a PCP guaranted to surpass it, I'd recommend going with a Marauder .25, FX Boss .30 or Daystate Wolverine (because of the magazines and listed by price). If you'd want to stay with .22 caliber look at the Hatsan AT44, Air Arms S510, or FX Royale 400/500 (again by price). If you prefer single load check out the Air Force Condor and Talon and if you want to stay with spring/gas-piston look at Weihrauch.